Terminal apparatus, base station apparatus, and method

ABSTRACT

A terminal apparatus for communicating with a base station apparatus is provided. The terminal apparatus includes a receiver configured to receive a Radio Resource Control (RRC) reconfiguration message including a parameter related to a first configuration from the base station apparatus, and a processing unit configured to perform configuration in accordance with the RRC reconfiguration message received. In a case that a first timer of an RRC protocol expires, a radio link failure of a source primary cell is not detected, and configuration related to Dual Active Protocol Stack (DAPS) handover is performed for the terminal apparatus, the processing unit reconfigures all of state variables configured for a Radio Link Control (RLC) entity of a Signaling Radio Bearer (SRB) in the source primary cell to respective initial values, resumes the SRB suspended in the source primary cell, and transmits an RRC message for notifying the base station apparatus that the DAPS handover has failed.

TECHNICAL FIELD

The present invention relates to a terminal apparatus, a base station apparatus, and a method. This application claims priority based on JP 2020-007313 filed on Jan. 21, 2020, the contents of which are incorporated herein by reference.

BACKGROUND ART

A radio access method and a radio network for cellular mobile communications (which will hereinafter be referred to as “Long Term Evolution (LTE; trade name)” or “Evolved Universal Terrestrial Radio Access (EUTRA)”) and a core network (which will be referred to as “Evolved Packet Core (EPC)”) have been studied by the 3rd Generation Partnership Project (3GPP). EUTRA is also referred to as E-UTRA.

Furthermore, as a radio access method and a radio network technology for a 5th generation cellular system, technical studies and standardization of LTE-Advanced Pro which is an enhanced technology of LTE and New Radio technology (NR) which is a new radio access technology have been conducted by the 3GPP (NPL 1). Furthermore, 5 Generation Core Network (5GC), which is a core network for the 5th generation cellular system, has also been studied (NPL 2).

CITATION LIST Non Patent Literature

-   NPL 1: 3GPP RP-170855, “Work Item on New Radio (NR) Access     Technology” -   NPL 2: 3GPP TS 23.501 v15.3.0, “System Architecture for the 5G     System; Stage 2” NPL 3: 3GPP TS 36.300 v15.3.0, “Evolved Universal     Terestrial Radio Access (E-UTRA) and Evolved Universal Terestrial     Radio Access Network (E-UTRAN); Overall description; Stage 2” -   NPL 4: 3GPP TS 36.331 v15.4.0, “Evolved Universal Terestrial Radio     Access (E-UTRA); Radio Resource Control (RRC); Protocol     specifications” -   NPL 5: 3GPP TS 36.323 v15.3.0, “Evolved Universal Terestrial Radio     Access (E-UTRA); Packet Data Convergence Protocol (PDCP)     specification” -   NPL 6: 3GPP TS 36.322 v15.3.0, “Evolved Universal Terestrial Radio     Access (E-UTRA); Radio Link Control (RLC) protocol specification” -   NPL 7: 3GPP TS 36.321 v15.3.0, “Evolved Universal Terestrial Radio     Access (E-UTRA); Medium Access Control (MAC) protocol specification” -   NPL 8: 3GPP TS 37.340v15.3.0, “Evolved Universal Terestrial Radio     Access (E-UTRA) and NR; Multi-Connectivity; Stage 2” -   NPL 9: 3GPP TS 38.300v 15.3.0, “NR; NR and NG-RAN Overall     description; Stage 2” NPL 10: 3GPP TS 38.331 v15.4.0, “NR; Radio     Resource Control (RRC); Protocol specifications” -   NPL 11: 3GPP TS 38.323 v15.3.0, “NR; Packet Data Convergence     Protocol (PDCP) specification” -   NPL 12: 3GPP TS 38.322 v15.3.0, “NR; Radio Link Control (RLC)     protocol specification” NPL 13: 3GPP TS 38.321 v15.3.0, “NR; Medium     Access Control (MAC) protocol specification” -   NPL 14: 3GPP TS 23.401 v15.0.0, “General Packet Radio Service (GPRS)     enhancements for Evolved Universal Terrestrial Radio Access Network     (E-UTRAN) access” -   NPL 15: 3GPP TS 23.502 v15.3.0, “Procedure for 5G System; Stage 2”     NPL 16: 3GPP TS 37.324 v15.1.0, “NR; Service Data Adaptation     Protocol (SDAP) Specification” -   NPL 17: 3GPP Draft_Report_v1.doc, “Report of 3GPP TSG RAN2 #105     meeting, Athens, Greece”     http://www.3gpp.org/ftp/TSG_RAN/WG2_RL2/TSGR2_105/Report/Draft_Report_v1.zip -   NPL 18: 3GPP RP-181544, “Revised WID: Even further mobility     enhancement in E-UTRAN” -   NPL 19: 3GPP RP-181433, “New WID: NR mobility enhancements” NPL 20:     3GPP R2-1901364, “Detail for non-split bearer option for     simultaneous connectivity” -   NPL 21: 3GPP TS 33.401 v15.9.0, “3GPP System Architecture Evolution     (SAE); Security architecture” -   NPL 22: 3GPP TS 33.501 v15.6.0, “Security architecture and     procedures for 5G System”

SUMMARY OF INVENTION Technical Problem

As a technical study for LTE, a mechanism for further expanding a mobility expansion technology for existing LTE has been under study. Furthermore, as a technical study for NR, a mechanism for further expanding a mobility expansion technology for existing NR has also been under study. (NPL 18, NPL 19). These studies include a study of a technology for making interruption of transmission and/or reception of user data closer to 0 ms mainly during movement between cells (during handover) while a base station apparatus and a terminal apparatus are connected (Reduce User Data Interruption (RUDI) and a study of handover robustness improvements.

For RUDI, a scheme (Dual Active Protocol Stack (DAPS)) for simultaneous presence of two protocol stacks for a single cell group has been under study. However, detailed operations of a terminal for efficiently controlling mobility have not yet been studied.

An aspect of the present invention has been made in light of the foregoing, and an object of the present invention is to provide a terminal apparatus, a base station apparatus, and a method that can efficiently control mobility.

Solution to Problem

In order to accomplish the object described above, an aspect of the present invention is contrived to provide the following means. Specifically, a terminal apparatus for communicating with a base station apparatus is provided. The terminal apparatus includes a receiver configured to receive, from the base station apparatus, a Radio Resource Control (RRC) reconfiguration message including a parameter related to a first configuration, and a processing unit configured to perform configuration in accordance with the RRC reconfiguration message received. In a case that a first timer of an RRC protocol expires, a radio link failure of a source primary cell is not detected, and configuration related to Dual Active Protocol Stack (DAPS) handover is performed for the terminal apparatus, the processing unit reconfigures all of state variables configured for a Radio Link Control (RLC) entity of a Signaling Radio Bearer (SRB) in the source primary cell to respective initial values, resumes the SRB suspended in the source primary cell, and transmits an RRC message for notifying the base station apparatus that the DAPS handover has failed.

In an aspect of the present invention, a base station apparatus for communicating with a terminal apparatus is provided. The base station apparatus includes a transmitter configured to transmit, to the terminal apparatus, a Radio Resource Control (RRC) reconfiguration message including a parameter related to a first configuration, and a processing unit configured to cause the terminal apparatus to perform configuration in accordance with the RRC reconfiguration message. In a case that a first timer of an RRC protocol expires, a radio link failure of a source primary cell is not detected, and configuration related to Dual Active Protocol Stack (DAPS) handover is performed for the terminal apparatus, the processing unit causes the terminal apparatus to reconfigure all of state variables configured for a Radio Link Control (RLC) entity of a Signaling Radio Bearer (SRB) in the source primary cell to respective initial values, resume the SRB suspended in the source primary cell, and transmit an RRC message for notifying the base station apparatus that the DAPS handover has failed.

Note that these comprehensive or specific aspects may be implemented in a system, an apparatus, a method, an integrated circuit, a computer program, or a recording medium, or may be implemented in any combination of systems, apparatuses, methods, integrated circuits, computer programs, and recording media.

Advantageous Effects of Invention

According to an aspect of the present invention, the terminal apparatus and the base station apparatus can implement efficient mobility processing.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of a communication system according to each embodiment of the present invention.

FIG. 2 is a diagram of protocol stacks of UP and CP of a terminal apparatus and a base station apparatus in E-UTRA according to each embodiment of the present invention.

FIG. 3 is a diagram of protocol stacks of the UP and the CP of the terminal apparatus and the base station apparatus in NR according to each embodiment of the present invention.

FIG. 4 is a diagram illustrating an example of a flow of a procedure for various configurations in an RRC 208 and/or an RRC 308 according to each embodiment of the present invention.

FIG. 5 is a block diagram illustrating a configuration of a terminal apparatus according to each embodiment of the present invention.

FIG. 6 is a block diagram illustrating a configuration of a base station apparatus according to each embodiment of the present invention.

FIG. 7 is a diagram illustrating an example of processing related to handover in EUTRA according to each embodiment of the present invention.

FIG. 8 is a diagram illustrating an example of processing related to handover in NR according to each embodiment of the present invention.

FIG. 9 is a diagram illustrating an example of conditions for start and stop of each timer according to an embodiment of the present invention.

FIG. 10 is a diagram illustrating an example of a mobilityControlInfo information element according to an embodiment of the present invention.

FIG. 11 is a diagram illustrating another example of the mobilityControlInfo information element according to an embodiment of the present invention.

FIG. 12 is a diagram illustrating an example of a Reconfiguration With Sync information element according to an embodiment of the present invention.

FIG. 13 is a diagram illustrating another example of the Reconfiguration With Sync information element according to an embodiment of the present invention.

FIG. 14 is a diagram illustrating an example of an ASN.1 notation included in a message related to reconfiguration of RRC connection in NR according to an embodiment of the present invention.

FIG. 15 is a diagram illustrating an example of an ASN.1 notation included in a message related to reconfiguration of RRC connection in E-UTRA according to an embodiment of the present invention.

FIG. 16 is a diagram illustrating an example of a flow of processing A according to an embodiment of the present invention.

FIG. 17 is a diagram illustrating an example of a flow of processing B according to an embodiment of the present invention.

FIG. 18 is a diagram illustrating an example of a flow of processing C according to an embodiment of the present invention.

FIG. 19 is a diagram illustrating an example of a flow of processing H according to an embodiment of the present invention.

FIG. 20 is a diagram illustrating an example of ASN.1 notation indicating a parameter for a configuration as to whether to apply a make before break-handover to a radio bearer according to each embodiment of the present invention.

FIG. 21 is diagram illustrating another example of ASN.1 notation indicating a parameter for a configuration as to whether to apply a make before break-handover to a radio bearer according to each embodiment of the present invention.

FIG. 22 is a diagram illustrating another example of a flow of processing E according to an embodiment of the present invention.

FIG. 23 is a diagram illustrating another example of a flow of processing B according to an embodiment of the present invention.

FIG. 24 is a diagram illustrating another example of a flow of processing LA according to an embodiment of the present invention.

FIG. 25 is a diagram illustrating an example of a processing method of a UE 122 according to each embodiment of the present invention.

FIG. 26 is a diagram illustrating another example of a processing method of the UE 122 according to each embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

LTE (and LTE-A Pro) and NR may be defined as different Radio Access Technologies (RATs). The NR may be defined as a technology included in the LTE. The LTE may be defined as a technology included in the NR. The LTE that is connectible to the NR by using Multi Radio Dual connectivity may be distinguished from the existing LTE. The LTE in which a 5GC is used as a core network may be distinguished from a conventional LTE, where an EPC is used as a core network. The present embodiment may be applied to the NR, the LTE and other RATs. Terms associated with the LTE and the NR are used in the following description. However, the present invention may be applied to other technologies using other terms. In the present embodiment, the term “E-UTRA” may be replaced with “LTE,” and the term “LTE” may be replaced with “E-UTRA.”

FIG. 1 is a schematic diagram of a communication system according to each embodiment of the present invention.

An E-UTRA 100 is a radio access technology described in NPL 3 or the like, and includes a cell group (CG) configured in one or multiple frequency bands. An E-UTRAN Node B (eNB) 102 is a base station apparatus of the E-UTRA 100. An Evolved Packet Core (EPC) 104 is a core network described in NPL 14 and the like and is designed as a core network for the E-UTRA 100. An interface 112 is an interface between the eNB 102 and the EPC 104, where there is a control plane (CP) through which control signals are transferred and a user plane (UP) through which user data is transferred.

An NR 106 is a radio access technology described in NPL 9 and the like, and includes a cell group (CG) including one or multiple frequency bands. A gNodeB (gNB) 108 is a base station apparatus in the NR 106. A 5GC 110 is a core network described in NPL 2 and the like, and is designed as a core network for the NR 106, but may also be used as a core network used for the E-UTRA 100 and including a function to connect to the 5GC 110. Hereinafter, the E-UTRA 100 may include the E-UTRA 100 including a function to connect to the 5GC 110.

An interface 114 is an interface between the eNB 102 and the 5GC 110, an interface 116 is an interface between the gNB 108 and the 5GC 110, an interface 118 is an interface between the gNB 108 and the EPC 104, an interface 120 is an interface between the eNB 102 and the gNB 108, and an interface 124 is an interface between the EPC 104 and 5GC 110. The interface 114, the interface 116, the interface 118, the interface 120, the interface 124, and the like may be interfaces that allow a CP only, an UP only, or both the CP and UP to pass through. The interface 114, the interface 116, the interface 118, the interface 120, the interface 124, and the like may be absent depending on a communication system provided by a network operator.

A UE 122 is a terminal apparatus supporting one or all of the E-UTRA 100 and the NR 106. As described in one or all of NPL 3 and NPL 9, in a case that the UE 122 connects to a core network via one or all of the E-UTRA 100 and the NR 106, a logical path called a radio bearer (RB) is established between the UE 122 and one or all of the E-UTRA 100 and the NR 106. The radio bearer used for the CP is referred to as a Signaling Radio Bearer (SRB), and the radio bearer used for the UP is referred to as a Data Radio Bearer (DRB). Each RB is assigned an RB identity (or an RB ID) and uniquely identified. The RB identity for the SRB is referred to as an SRB identity (or an SRB ID), and the RB identity for the DRB is referred to as a DRB identity (or a DRB ID).

As described in NPL 3, in a case that a connection destination core network for the UE 122 is an EPC 104, each DRB established between the UE 122 and any or all of the E-UTRA 100 and the NR 106 is uniquely linked to each Evolved Packet System (EPS) bearer passing through the EPC 104. Each EPS bearer is assigned an EPS bearer identity (or ID), and uniquely identified. Additionally, identical QoS is ensured for data passing through an identical EPS bearer.

As described in NPL 9, in a case that a connection destination core network of the UE 122 is the 5GC 110, one or multiple DRBs established between the UE 122 and one or all of the E-UTRA 100 and the NR 106 are further linked to one of the Packet Data Unit (PDU) sessions established in the 5GC 110. One or multiple QoS flows are present in each PDU session. Each DRB may be mapped to one or multiple QoS flows present in the linked PDU session or to none of the QoS flows. Each PDU session is identified by a PDU session identity (or ID). Additionally, each QoS flow is identified by a QoS flow identity. Identical QoS is ensured for data passing through an identical QoS flow.

In the EPC 104, any of the PDU sessions and the QoS flows is absent or none of the PDU sessions and the QoS flows are present. No EPS bearers are present in the 5GC 110. In other words, in a case of being connected to the EPC 104, the UE 122 has information of the EPS bearers. In a case of being connected to the 5GC 110, the UE 122 has information of any or all of the PDU sessions and the QoS flows.

FIG. 2 is a diagram of protocol stacks of UP and CP of a terminal apparatus and a base station apparatus in an E-UTRA radio access layer according to each embodiment of the present invention.

FIG. 2(A) is a diagram of a protocol stack of the UP used in a case that the UE 122 communicates with the eNB 102 in the E-UTRA 100.

A Physical layer (PHY) 200 is a radio physical layer and provides a transmission service to an upper layer by using a physical channel. The PHY 200 is connected with a Medium Access Control layer (MAC) 202 of an upper layer to be described below via transport channels. Data is exchanged between the MAC 202 and the PHY 200 via the transport channels. The data is transmitted and/or received via radio physical channels between the PHYs of the UE 122 and the eNB 102.

The MAC 202 is a medium access control layer that maps various logical channels to various transport channels. The MAC 202 is connected with a radio link control layer (RLC) 204 of an upper layer to be described below via logical channels. The major classifications of the logical channel depend on the type of information to be transmitted, specifically, the logical channels are classified into control channels for transmitting control information and traffic channels for transmitting user information. The MAC 202 has a function of controlling the PHY 200 in order to perform the Discontinuous Reception and Transmission (DRX and DTX), a function of performing a random access procedure, a function of reporting transmit power information, a function of performing HARQ control, and the like (NPL 7).

An RLC 204 is a radio link control layer that segments data received from a Packet Data Convergence Protocol Layer (PDCP) 206 corresponding to an upper layer described below and that adjusts the data size such that a lower layer can properly transmit the data. The RLC 204 has three modes, namely a Transparent Mode (TM), an Unacknowledged Mode (UM), and an Acknowledged Mode (AM). In the TM, segmentation of data received from an upper layer is not performed, and addition of an RLC header is not performed. In the UM, segmentation of data received from an upper layer, addition of an RLC header, and the like are performed, but retransmission control of data is not performed. In the AM, segmentation of data received from an upper layer, addition of an RLC header, retransmission control of data, and the like are performed. A retransmission control function may be a function for ensuring Quality of Service (QoS) required by each piece of data. In performing retransmission control of data, information of unreached data that is transmitted from a reception side of RLC to a transmission side thereof is referred to as a status report. An indication for prompting a status report that is transmitted from a transmission side of RLC to a reception side thereof is referred to as a poll. Note that data transmitted to a lower layer in TM may be referred to as TMD PDU, data transmitted to a lower layer in UM may be referred to as UMD PDU, and data transmitted to a lower layer in AM may be referred to as AMD PDU. (NPL 6).

The PDCP 206 is a packet data convergence protocol layer for efficiently transmitting user data such as IP packets in wireless sections. The PDCP 206 may include a header compression function to compress unnecessary control information. The PDCP 206 may also include a data ciphering function. (NPL 5).

Note that data processed in the MAC 202, the RLC 204, and the PDCP 206 are referred to as a MAC Protocol Data Unit (PDU), an RLC PDU, and a PDCP PDU, respectively. Data delivered from an upper layer to the MAC 202, the RLC 204, and the PDCP 206 or data delivered therefrom to an upper layer are respectively referred to as a MAC Service Data Unit (SDU), an RLC SDU, and a PDCP SDU. A segmented RLC SDU is referred to as an RLC SDU segment.

For distinction between PDCP PDUs for data and PDCP PDUs for control, PDCP PDUs may also be referred to as PDCP Data PDUs (PDCP DATA PDUs) and PDCP Control PDUs (PDCP CONTROL PDUs), respectively. For distinction between RLC PDUs for data and RLC PDUs for control, RLC PDUs may also be referred to as RLC Data PDUs (RLC DATA PDUs) and RLC Control PDUs (RLC CONTROL PDUs), respectively.

FIG. 2(B) is a protocol stack diagram of the CP used by the UE 122 in communicating with the eNB 102 and a Mobility Management Entity (MME) used as a logical node providing functions such as authentication and mobility management in the E-UTRA 100.

In the protocol stack of the CP, a Radio Resource Control layer (RRC) 208 and a non Access Strarum (NAS) 210 are present in addition to the PHY 200, the MAC 202, the RLC 204, and the PDCP 206. The RRC 208 is a radio link control layer that performs processing such as establishment, re-establishment, suspension, and resumption of an RRC connection, reconfiguration of the RRC connection, for example, configuration of the radio bearer (RB) and the cell group such as establishment, change, or release, control of logical channels, transport channels, physical channels, and the like, and further performs configuration of handover and measurement, and the like. The RBs may be classified into a Signaling Radio Bearer (SRB) and a Data Radio Bearer (DRB), and the SRB may be used as a path for transmitting an RRC message which is control information. The DRB may be used as a path for transmitting the user data. Each RB may be configured between the RRCs 208 of the eNB 102 and the UE 122. A portion of the RB including the RLC 204 and the logical channel may be referred to as an RLC bearer (NPL 4). In contrast to the NAS layer carrying signals between the MME and the UE 122, some or all of the layers of the PHY 200, the MAC 202, the RLC 204, the PDCP 206, and the RRC 208 carrying signals and data between the UE 122 and the eNB 102 may be referred to as Access Strarum (AS) layers.

The functional classification of the MAC 202, the RLC 204, the PDCP 206, and the RRC 208 described above is an example, and some or all of the respective functions may not be implemented. Some or all of the functions of each layer may be included in another layer.

Note that an IP layer, and a Transmission Control Protocol (TCP) layer, a User Datagram Protocol (UDP) layer, an application layer, and the like that are upper layers of the IP layer are upper layers of the PDCP layer (not illustrated). The RRC layer and the non Access Strarum (NAS) layer also correspond to upper layers of the PDCP layer (this is not illustrated). In other words, the PDCP layer is a lower layer of the RRC layer, the NAS layer, and the IP layer, and the Transmission Control Protocol (TCP) layer, the User Datagram Protocol (UDP) layer, and the application layer that are upper layers of the IP layer.

FIG. 3 is a diagram of protocol stacks of UP and CP of a terminal apparatus and a base station apparatus in an NR radio access layer according to each embodiment of the present invention.

FIG. 3(A) is a diagram of the protocol stack of the UP used by the UE 122 in communicating with the gNB 108 in the NR 106.

A physical layer (PHY) 300 is a radio physical layer of the NR and may provide a transmission service to an upper layer by using a physical channel. The PHY 300 may be connected with the Medium Access Control layer (MAC) 302 of an upper layer to be described below via the transport channels. Data may be exchanged between the MAC 302 and the PHY 300 via the transport channels. The data may be transmitted and/or received between the PHYs of the UE 122 and the gNB 108 via the radio physical channel.

Now, the physical channels will be described.

The following physical channels may be used for the radio communication between the terminal apparatus and the base station apparatus.

-   -   Physical Broadcast CHannel (PBCH)     -   Physical Downlink Control CHannel (PDCCH)     -   Physical Downlink Shared CHannel (PDSCH)     -   Physical Uplink Control CHannel (PUCCH)     -   Physical Uplink Shared CHannel (PUSCH)     -   Physical Random Access CHannel (PRACH)

The PBCH is used to broadcast system information required by the terminal apparatuses.

The PBCH may be used to broadcast time indexes (SSB-Indexes) within the periodicity of synchronization signal blocks (also referred to as SS/PBCH blocks) in NR.

The PDCCH is used to transmit (or carry) downlink control information (DCI) in a case of downlink radio communication (radio communication from the base station apparatus 3 to the terminal apparatus). Here, one or multiple pieces of DCI (which may be referred to as DCI formats) are defined for transmission of the downlink control information. In other words, a field for the downlink control information is defined as DCI and is mapped to information bits. The PDCCH is transmitted in a PDCCH candidate. The terminal apparatus monitors a set of PDCCH candidates in the serving cell. The monitoring means an attempt to decode the PDCCH in accordance with a certain DCI format. The certain DCI format may be used for scheduling of the PUSCH in the serving cell. The PUSCH may be used for transmission of user data, transmission of RRC messages, and the like.

The PUCCH is used to transmit Uplink Control Information (UCI) in a case of uplink radio communication (radio communication from the terminal apparatus to the base station apparatus). Here, the uplink control information may include Channel State Information (CSI) used to indicate a downlink channel state. The uplink control information may include Scheduling Request (SR) used to request an UL-SCH resource. The uplink control information may include a Hybrid Automatic Repeat request ACKnowledgement (HARQ-ACK).

The PDSCH may be used to transmit downlink data (Downlink Shared CHannel (DL-SCH)) from the MAC layer. In a case of the downlink, the PDSCH is also used to transmit System Information (SI), a Random Access Response (RAR), and the like.

The PUSCH may be used to transmit uplink data (Uplink-Shared CHannel (UL-SCH)) from the MAC layer or to transmit the HARQ-ACK and/or CSI along with the uplink data. The PSCH may be used to transmit the CSI only or the HARQ-ACK and CSI only. In other words, the PSCH may be used to transmit the UCI only. The PDSCH or the PUSCH may be used to transmit RRC signaling (also referred to as RRC messages) and MAC control elements. In this regard, in the PDSCH, the RRC signaling transmitted from the base station apparatus may be signaling common to multiple terminal apparatuses in a cell. The RRC signaling transmitted from the base station apparatus may be dedicated signaling for a certain terminal apparatus (also referred to as dedicated signaling). In other words, terminal apparatus-specific (UE-specific) information may be transmitted through dedicated signaling to the certain terminal apparatus. The PUSCH may be used to transmit UE capabilities in the uplink.

The PRACH may be used for transmitting a random access preamble. The PRACH may be used for indicating the initial connection establishment procedure, the handover procedure, the connection re-establishment procedure, synchronization (timing adjustment) for uplink transmission, and a request for a PUSCH (UL-SCH) resource.

The MAC 302 is a medium access control layer that maps various logical channels to various transport channels. The MAC 302 may be connected with a Radio Link Control layer (RLC) 304 of a high layer to be described below via the logical channels. The classification of the logical channel depends on the type of information to be transmitted, and the logical channels may be classified into the control channels for transmitting the control information and the traffic channels for transmitting the user information. The MAC 302 may have a function of controlling the PHY 300 in order to perform the Discontinuous Reception and Transmission (DRX and DTX), a function of performing the random access procedure, a function of reporting the transmit power information, a function of performing the HARQ control, and the like (NPL 13).

The RLC 304 is a radio link control layer that segments data received from a Packet Data Convergence Protocol Layer (PDCP) 306 corresponding to an upper layer described below and that adjusts the data size such that a lower layer can properly transmit the data. The RLC 304 has three modes, namely a Transparent Mode (TM), an Unacknowledged Mode (UM), and an Acknowledged Mode (AM). In the TM, segmentation of data received from an upper layer is not performed, and addition of an RLC header is not performed. In the UM, segmentation of data received from an upper layer, addition of an RLC header, and the like are performed, but retransmission control of data is not performed. In the AM, segmentation of data received from an upper layer, addition of an RLC header, retransmission control of data, and the like are performed. A retransmission control function may be a function for ensuring Quality of Service (QoS) required by each piece of data. In performing retransmission control of data, information of unreached data that is transmitted from a reception side of RLC to a transmission side thereof is referred to as a status report. An indication for prompting a status report that is transmitted from a transmission side of RLC to a reception side thereof is referred to as a poll. Note that data transmitted to a lower layer in TM may be referred to as TMD PDU, data transmitted to a lower layer in UM may be referred to as UMD PDU, and data transmitted to a lower layer in AM may be referred to as AMD PDU. (NPL 12).

The PDCP 306 is a packet data convergence protocol layer for efficiently transmitting user data such as IP packets in wireless sections. The PDCP 306 may include a header compression function to compress unnecessary control information. The PDCP 306 may also include a data ciphering function and a data integrity protection function (NPL 11).

A Service Data Adaptation Protocol (SDAP) 310 is a service data adaptation protocol layer that functions to map the DRB to a downlink QoS flow transmitted from the 5GC 110 to the terminal apparatus via the base station apparatus, and to map the DRB to an uplink QoS flow transmitted from the terminal apparatus to the 5GC 110 via the base station apparatus, and to store mapping rule information (NPL 16).

Note that the data processed in the MAC 302, the RLC 304, the PDCP 306, and the SDAP 310 are referred to as a MAC Protocol Data Unit (PDU), an RLC PDU, a PDCP PDU, and an SDAP PDU, respectively. Data delivered from an upper layer to the MAC 302, the RLC 304, the PDCP 306, and the SDAP 310 or data delivered therefrom to an upper layer are respectively referred to as a MAC Service Data Unit (SDU), an RLC SDU, a PDCP SDU, and an SDAP SDU. A segmented RLC SDU is referred to as an RLC SDU segment.

For distinction between SDAP PDUs for data and SDAP PDUs for control, SDAP PDUs may also be referred to as SDAP Data PDUs (SDAP DATA PDUs) and SDAP Control PDUs (SDAP CONTROL PDUs), respectively. For distinction between PDCP PDUs for data and PDCP PDUs for control, PDCP PDUs may also be referred to as PDCP Data PDUs (PDCP DATA PDUs) and PDCP Control PDUs (PDCP CONTROL PDUs), respectively. For distinction between RLC PDUs for data and RLC PDUs for control, RLC PDUs may also be referred to as RLC Data PDUs (RLC DATA PDUs) and RLC Control PDUs (RLC CONTROL PDUs), respectively.

FIG. 3(B) is a protocol stack diagram of the CP used by the UE 122 in communicating with the gNB 108 and an Access and Mobility Management function (AMF) used as a logical node providing functions such as authentication and mobility management in the NR 106.

In the protocol stack of the CP, a Radio Resource Control layer (RRC) 308 and a non Access Strarum (NAS) 312 are present in addition to the PHY 300, the MAC 302, the RLC 304, and the PDCP 306. The RRC 308 is a radio link control layer that performs processing such as establishment, re-establishment, suspension, resumption, and the like of an RRC connection, reconfiguration of the RRC connection, for example, configuration of the radio bearer (RB) and the cell group such as establishment, change, or release, control of logical channels, transport channels, and physical channels, and the like, and further performs configuration of handover and measurement, and the like. The RBs may be classified into a Signaling Radio Bearer (SRB) and a Data Radio Bearer (DRB), and the SRB may be used as a path for transmitting an RRC message which is control information. The DRB may be used as a path for transmitting the user data. Each RB may be configured between RRCs 308 of the gNB 108 and the UE 122. A portion of the RB including the RLC 304 and the logical channel may be referred to as an RLC bearer (NPL 10). In contrast to the NAS layer carrying signals between the AMF and the UE 122, some or all of the layers of the PHY 300, the MAC 302, the RLC 304, the PDCP 306, the RRC 308, and the SDAP 310 carrying signals and data between the UE 122 and the gNB 108 may be referred to as Access Strarum (AS) layers.

For the SRB, SRB0 to SRB3 described below may be defined. SRB0 may be an SRB used for an RRC message and using a Common Control CHannel (CCCH) corresponding to a logical channel SRB1 may be an SRB for the RRC message (which may include a piggybacked NAS message) and for the NAS message prior to the establishment of SRB2, and the Dedicated Control CHannel (DCCH) corresponding to a logical channel may be used for all cases. SRB2 may be an SRB for the NAS message, and the DCCH corresponding to a logical channel may be used for all cases. SRB2 may have a lower priority than SRB1. SRB3 may be an SRB for a particular RRC message in a case that the UE 122 is configured with EN-DC, NGEN-DC, NR-DC, or the like, and the DCCH corresponding to a logical channel may be used for all cases. Other SRBs may also be provided for other applications.

The functional classification of the MAC 302, the RLC 304, the PDCP 306, the SDAP 310, and the RRC 308 described above is an example, and some or all of the functions may not be implemented. Some or all of the functions of each layer may be included in another layer.

Note that an upper layer (not illustrated) of the AS layer may be referred to as a PDU layer, as described in NPL 2. The PDU layer may include any or all of an IP layer, a Transmission Control Protocol (TCP) layer and a User Datagram Protocol (UDP) layer that are upper layers of the IP layer, or other layers. The application layer may be an upper layer of the PDU layer or may be included in the PDU layer. Note that the PDU layer may be an upper layer with respect to the user plane of the AS layer. The RRC layer and the non Access Strarum (NAS) layer may also be an upper layer of one or all of the SDAP layer and the PDCP layer (this is not illustrated). In other words, one or all of the SDAP layer and the PDCP layer are lower layers of any or all of the RRC layer, the NAS layer, and the IP layer, and the Transmission Control Protocol (TCP) layer, the User Datagram Protocol (UDP) layer, and the application layer that are upper layers of the IP layer.

Note that, in each embodiment of the present invention, any or all of the following may belong to the application layer: a Session Initiation Protocol (SIP), a Session Description Protocol (SDP), and the like used for IMS; a Real-time Transport Protocol (RTP), a Real-time Transport Control Protocol (RTCP), a HyperText Transfer Protocol (HTTP), and the like used for media communication or media communication control; and codecs of various media and the like.

Note that the RRC layer of the terminal apparatus may perform any or all of establishment, configuration, and control on the physical layer, the MAC layer, the RLC layer, the PDCP layer, and the SDAP layer of the terminal apparatus. The RRC layer of the terminal apparatus may establish and/or configure the physical layer, the MAC layer, the RLC layer, the PDCP layer, and the SDAP layer in accordance with the RRC message transmitted from the RRC layer of the base station apparatus. The MAC layer, the RLC layer, the PDCP layer, and the SDAP layer may respectively be referred to as a MAC sublayer, an RLC sublayer, a PDCP sublayer, and a SDAP sublayer.

Note that an entity may refer to each of the layers belonging to the AS layer configured for one or all of the terminal apparatus and the base station apparatus or the function of each layer. Specifically, the physical layer (PHY layer), the MAC layer, the RLC layer, the PDCP layer, the SDAP layer, and the RRC layer, on which any or all of establishment, configuration, and control is performed for one or all of the terminal apparatus and the base station apparatus, or the functions of the respective layers may be referred to as a physical entity (PHY entity), a MAC entity, an RLC entity, a PDCP entity, an SDAP entity, and an RRC entity. One or multiple entities may be included in each layer. Any or all of establishment, configuration, and control may be performed on the PDCP entity and the RLC entity for each radio bearer. Any or all of establishment, configuration, and control may be performed on the MAC entity for each cell group. Any or all of establishment, configuration, and control may be performed on the SDAP entity for each PDU session.

Note that a COUNT value may be used in a case that processing for ciphering or integrity protection is performed in the PDCP layer or the PDCP entity. The COUNT value may include a Hyper Frame Number (HFN) and a Sequence Number (SN) added to the header of the PDCP PDU. The sequence number may be incremented by one each time a PDCP DATA PDU is generated by the PDCP layer or PDCP entity on the transmission side. The HFN may be incremented by one each time the sequence number reaches the maximum value.

Note that in each embodiment of the present invention, for a distinction between the E-UTRA protocol and the NR protocol, the MAC 202, the RLC 204, the PDCP 206, and the RRC 208 may be respectively referred to as a MAC for E-UTRA or a MAC for LTE, an RLC for E-UTRA or an RLC for LTE, a PDCP for E-UTRA or a PDCP for LTE, and an RRC for E-UTRA or an RRC for LTE. Furthermore, the MAC 302, the RLC 304, the PDCP 306, and the RRC 308 may also be referred to as MAC for NR, RLC for NR, RLC for NR, and RRC for NR, respectively. Alternatively, there may be descriptions using a space such as an E-UTRA PDCP or an LTE PDCP, an NR PDCP, and the like.

As also illustrated in FIG. 1 , the eNB 102, the gNB 108, the EPC 104, and the 5GC 110 may be connected to one another via the interface 112, the interface 116, the interface 118, the interface 120, and the interface 114. Thus, the RRC 208 in FIG. 2 may be replaced with the RRC 308 in FIG. 3 to support various communication systems. Furthermore, the PDCP 206 in FIG. 2 may also be replaced with the PDCP 306 in FIG. 3 . The RRC 308 in FIG. 3 may include the function of the RRC 208 in FIG. 2 . Furthermore, the PDCP 306 in FIG. 3 may be the PDCP 206 in FIG. 2 . In the E-UTRA 100, the NR PDCP may be used as a PDCP even in a case that the UE 122 communicates with the eNB 102.

The state transition of the UE 122 in LTE and NR will now be described. The UE 122 connected to the EPC or the 5GC may be in an RRC_CONNECTED state in a case that an RRC connection has been established. A state in which RRC connection has been established may include a state in which the UE 122 retains a part or all of a UE context to be described later. Further, a state in which RRC connection has not been established may include a state in which the UE 122 can transmit and/or receive unicast data. The UE 122 may be in an RRC_INACTIVE state in a case that the RRC connection is suspended (in a case that the UE 122 is connected to the 5GC). In the other cases, the UE 122 may be in an RRC_IDLE state.

Note that the UE 122 connected to the EPC does not have the RRC_INACTIVE state but that the E-UTRAN may initiate suspension of the RRC connection. In this case, in response to suspension of the RRC connection, the UE 122 transitions to the RRC_IDLE state while retaining an AS context of the UE and an identity used for resumption (resumeIdentity). In a case that the UE 122 retains the AS context of the UE and that the E-UTRAN permits the RRC connection to be resumed and that the UE 122 needs to transition from the RRC_IDLE state to the RRC_CONNECTED state, the resumption of the RRC connection suspended may be initiated by the upper layer (e.g., the NAS layer).

In other words, the definition of the suspension may vary between the UE 122 connected to the EPC and the UE 122 connected to the 5GC. All or part of the procedure for resuming the connection suspended may vary between a case where the UE 122 is connected to the EPC (the connection is suspended in the RRC_IDLE state) and a case where the UE 122 is connected to the 5GC (the connection is suspended in the RRC_INACTIVE state).

Note that the RRC_CONNECTED state, the RRC_INACTIVE state, and the RRC_IDLE state may be respectively referred to as a connected state (connected mode), an inactive state (inactive mode), and an idle state (idle mode), or may be respectively referred to as an RRC connected state (RRC connected mode), an RRC inactive state (RRC inactive mode), and an RRC idle state (RRC idle mode).

The AS context of the UE retained by the UE 122 may be information including all or some of a current RRC configuration, a current security context, a PDCP state including a RObust Header Compression (ROHC) state, a Cell Radio Network Temporary Identifier (C-RNTI) used in a PCell of a connection source, a cell identity (cellIdentity), and a physical cell identity of the PCell of the connection source. Note that the AS context of the UE retained by one or all of the eNB 102 and the gNB 108 may include information identical to the information of the AS context of the UE retained by the UE 122, or may include information different from the information included in the AS context of the UE retained by the UE 122.

The security context may be information including all or some of a ciphering key at the AS level, a Next Hop parameter (NH), a Next Hop Chaining Counter parameter (NCC) used to derive an access key for the next hop, an identifier of a ciphering algorithm at a selected AS level, and a counter used for replay protection.

Next, the handover in LTE and NR will be described. The handover may be processing in which the UE 122 in the RRC connected state changes the serving cell. The handover may be performed in a case that the UE 122 receives an RRC message for indicating a handover from the eNB 102 and/or the gNB 108. The RRC message for indicating a handover may be a message related to reconfiguration of RRC connection including a parameter for indicating handover (for example, an information element referred to as MobilityControlInfo described in NPL 4, or an information element referred to as ReconfigurationWithSync described in NPL 10), or may be a message indicating movement to a cell of another RAT (for example, MobilityFromEUTRACommand described in NPL 4, or MobilityFromNRCommand described in NPL 10). A condition that the UE 122 can perform handover may include a part or all of a case that AS security is activated, SRB2 is established, and at least one DRB is established.

FIG. 4 is a diagram illustrating an example of a flow of a procedure for various configurations in the RRC 208 and/or the RRC 308 according to each embodiment of the present invention. FIG. 4 is an example of a flow in a case that an RRC message is sent from the base station apparatus (eNB 102 and/or gNB 108) to the terminal apparatus (UE 122).

In FIG. 4 , the base station apparatus creates an RRC message (step S400). The creation of the RRC message in the base station apparatus may be performed in a case that the base station apparatus distributes broadcast information (System Information (SI)) or paging information, or in a case that the base station apparatus determines a need to cause a particular terminal apparatus to perform processing, for example, configuration related to security, reconfiguration of an RRC connection (processing (establishment, change, release, or the like) of the radio line bearer, processing (establishment, addition, change, release, or the like) of the cell group, measurement configuration, handover configuration, or the like), release of the RRC connected state, or the like. Additionally, the RRC message may be used for a command for handover to a different RAT. The RRC message includes information (parameters) for various information notifications and configurations. In specifications related to RRC in NPL 4, NPL 10, or the like, the above-described parameters are referred to as fields and/or information elements, and are notated by using a notation method referred to as Abstract Syntax Notation One (ASN.1).

In FIG. 4 , the base station apparatus then transmits the RRC message created, to the terminal apparatus (step S402). Then, in a case that processing such as a configuration is necessary in accordance with the RRC message received, the terminal apparatus performs the processing (step S404).

Note that the creation of the RRC message is not limited to the example described above, and may be performed for other purposes, as described in NPL 4, NPL 10, and the like.

For example, the RRC message may be used for configuration related to Dual Connectivity (DC) or Multi-Radio Dual Connectivity (MR-DC) described in NPL 8.

The Dual Connectivity (DC) may be a technology for performing data communication by using radio resources of both cell groups including a master cell group (MCG) including master nodes (MNs) and a secondery cell group (SCG) including secondery nodes (SNs), each cell group including two base station apparatuses (nodes). The master node and the secondary node may be an identical node (identical base station apparatus). Furthermore, the MR-DC described in NPL 8 may be a technology in which cells of both Radio Access Technologies (RATs) of E-UTRA and NR are formed into cell groups for each RAT, which are assigned to the UE, and in which data communication is performed by utilizing radio resources of both MCG and SCG. In the MR-DC, the master node may be a base station including primary RRC functions related to MR-DC, for example, functions to add a secondary node, to establish, change, and release an RB, to add, change, and release an MCG, and to perform handover and the like, and the secondary base station may be a base station including some RRC functions, for example, functions to change and release an SCG, and the like.

In the MR-DC described in NPL 8, the RRC corresponding to the master node side RAT may be used to configure both the MCG and the SCG. For example, in E-UTRA-NR Dual Connectivity (EN-DC) corresponding to the MR-DC in which the EPC 104 is used as a core network and the eNB 102 (also referred to as an evolved eNB 102) is used as a master node and in NG-RAN E-UTRA-NR Dual Connectivity (NGEN-DC) corresponding to the MR-DC in which the 5GC 110 is used as a core network and the eNB 102 is used as a master node, an RRC message for E-UTRA described in NPL 4 may be transmitted and received between the eNB 102 and the UE 122. In this case, the RRC message may include NR configuration information described in NPL 10 as well as LTE (E-UTRA) configuration information. Additionally, the RRC message transmitted from the eNB 102 to the UE 122 may be transmitted from the eNB 102 to the UE 122 via the gNB 108. The configuration of the present RRC message may be used in E-UTRA/5GC (option 5 described in NPL 17) corresponding to non-MR-DC in which the eNB 102 (evolved eNB) uses the 5GC as a core network.

Additionally, in contrast, in the MR-DC described in NPL 8, in NR-E-UTRA Dual Connectivity (NE-DC) corresponding to the MR-DC in which the 5GC 110 is used as a core network and the gNB 108 is used as a master node, an RRC message for NR described in NPL 10 may be transmitted and received between the gNB 108 and the UE 122. In this case, the RRC message may include LTE (E-UTRA) configuration information described in NPL 4 as well as NR configuration information. Additionally, the RRC message transmitted from the gNB 108 to the UE 122 may be transmitted from the gNB 108 to the UE 122 via the eNB 102.

Note that the embodiment is not limited to the case of utilization of the MR-DC and that the RRC message for E-UTRA transmitted from the eNB 102 to the UE 122 may include an RRC message for NR, whereas or the RRC message for NR transmitted from the gNB 108 to the UE 122 may include an RRC message for E-UTRA.

A network configuration in which the eNB 102 is used as a master node and the EPC 104 is used as a core network may be referred to as E-UTRA/EPC. Additionally, a network configuration in which the eNB 102 is used as a master node and the 5GC 110 is used as a core network may be referred to as E-UTRA/5GC. In addition, a network configuration in which the gNB 108 is used as a master node and the 5GC 110 is used as a core network may be referred to as NR or NR/5GC. Moreover, this designation need not be limited to a case where the DC is configured. In the case that the DC is not configured, the above-described master node may refer to a base station apparatus that communicates with the terminal apparatus.

FIG. 14 is an example of an ASN.1 notation expressing any or all of the fields and information elements related to a radio bearer configuration, the ASN.1 notation being included in a message related to reconfiguration of RRC connection in NR in FIG. 4 . FIG. 15 is an example of an ASN.1 notation expressing any or all of the fields and information elements related to a radio bearer configuration, the ASN.1 notation being included in a message related to reconfiguration of RRC connection in E-UTRA in FIG. 4 . Not only in FIG. 14 and FIG. 15 , but in examples of the ASN.1 according to an embodiment of the present invention, <omitted> and <partly omitted> are not a part of the notation of the ASN.1 but indicate that other information is omitted at these positions. Note that there may also be omitted information elements in a part where neither <omitted> nor <partly omitted> is indicated. Note that, in an embodiment of the present invention, the examples of ASN.1 do not correctly follow the ASN.1 notation method but represent examples parameters of a message for reconfiguration of RRC connection according to an embodiment of the present invention and that any other designation and any other notation may be used. The examples of ASN.1 correspond to only examples related to main information closely associated with an aspect of the present invention in order to avoid complicated description. Note that the parameters notated in ASN.1 may all be referred to as information elements without distinction between fields, information elements, or the like. In an embodiment of the present invention, the parameters such as fields and information elements notated in ASN.1, the parameters being included in the RRC message, may also be referred to as information. Note that the message related to reconfiguration of RRC connection may be an RRC reconfiguration message in NR or an RRC connection reconfiguration message in E-UTRA.

In FIG. 14 , the information element represented by RadioBearerConfig is an information element related to configurations of radio bearers such as SRBs or DRBs and include PDCP configuration information elements and SDAP configuration information elements to be described below. An information element represented by SRB-ToAddMod and included in the information elements represented by RadioBearerConfig may be information indicating a signaling radio bearer (SRB) configuration, and may also be referred to as an SRB configuration information element or a signaling radio bearer configuration information element. An information element represented by SRB-ToAddModList may be a list of pieces of information indicating SRB configurations. An information element represented by DRB-ToAddMod and included in the information elements represented by RadioBearerConfig may be information indicating a data radio bearer (DRB) configuration, and may also be referred to as a DRB configuration information element or a data radio bearer configuration information element. An information element represented by DRB-ToAddModList may be a list of pieces of information indicating DRB configurations. Note that any or all of the SRB configurations and the DRB configurations may be referred to as radio bearer configurations.

An information element included in the SRB configuration information elements and represented by SRB-Identity is information of SRB identity of an SRB to be added or changed, and may be an identifier that uniquely identifies the SRB at each terminal apparatus. This information element may be replaced with an SRB identity information element, a radio bearer identity information element, or a signaling radio bearer identity information element.

An information element included in the DRB configuration information elements and represented by DRB-Identity is an information of DRB identity of a DRB to be added or changed, and may be an identifier that uniquely identifies the DRB at each terminal apparatus. This information element may be replaced with a DRB identity information element, a radio bearer identity information element, or a data radio bearer identity information element. In the example illustrated in FIG. 14 , the DRB identity has an integer value ranging from 1 to 32. However, the DRB identity may take another value. In a case of DC, the DRB identity is unique within the scope of the UE 122.

An information element included in the DRB configuration information elements and represented by cnAssociation may be an information element indicating whether the EPC 104 or the 5GC 110 is used as a core network, and may also be referred to as a core network association information element. In other words, in a case that the UE 122 is connected to the EPC, the DRB may be associated with an EPS bearer identity information element (eps-BearerIdentity) in cnAssociation or with an EPS bearer identity corresponding to the value of the EPS bearer identity information element. In a case that the UE 122 is connected to the 5GC 110, the DRB may be associated with an SDAP entity configured in accordance with an SDAP configuration information element (sdap-Config) described below, or a PDU session information element described below and included in the SDAP configuration information element, or a PDU session identity corresponding to the value of the PDU session information element, or a PDU session indicated by the PDU session information element. In other words, the information represented by cnAssociation may include an EPS bearer identity information element (eps-BearerIdentity) in a case that the EPC 104 is used as a core network, such as in a case of using EN-DC, and may include an information element (sdap-Config) indicating an SDAP configuration in a case that the 5GC 110 is used as a core network, in other words, in a case of not using EN-DC.

The information element represented by sdap-Config may be information related to a configuration or reconfiguration of the SDAP entity that determines a mapping method between the QoS flow and the DRB in a case that the 5GC 110 is used as a core network, and may be replaced with an SDAP configuration information element.

A field or an information element included in the SDAP configuration information elements and represented by pdu-session or PDU-SessionID may be the PDU session identity of a PDU session described in NPL 2 and to which the QoS flow mapped to the radio bearer corresponding to the value of the radio bearer identity information element belongs, the radio bearer identity information element being included in the DRB configuration information elements including the present SDAP configuration information element, and may be replaced with a PDU session identity information element. The value of the PDU session identity information element may be an integer that is not negative. Additionally, at each of the terminal apparatuses, multiple DRB identities may correspond to one PDU session identity.

An information element included in the SDAP configuration information elements and indicated by mappedQoS-FlowsToAdd may be information indicating a list of QoS flow identity (QFI) information elements described below of QoS flows to be mapped to or additionally mapped to the radio bearer corresponding to the value of the radio bearer identity information element included in the DRB configuration information elements including the present SDAP configuration information elements, and may be replaced with an added QoS flow information element. The QoS flow described above may be a QoS flow of a PDU session indicated by the PDU session information element included in the present SDAP configuration information elements.

An information element included in the SDAP configuration information elements and indicated by mappedQoS-FlowsToRelease may be information indicating a list of QoS flow identity (QFI) information elements described below of QoS flows from which a mapping relationship is to be released and which are included in the QoS flows mapped to the radio bearer corresponding to the value of the radio bearer identity information element included in the DRB configuration information elements including the present SDAP configuration information elements, and may be replaced with a released QoS flow information element. The QoS flow described above may be a QoS flow of a PDU session indicated by the PDU session information element included in the present SDAP configuration information elements.

An information element indicated by QFI may be a QoS flow identity described in NPL 2 and uniquely identifying a QoS flow, and may be replaced with a QoS flow identity information element. The value of the QoS flow identity information element may be an integer that is not negative. The value of the QoS flow identity information element may be unique to the PDU session.

Furthermore, the SDAP configuration information elements may include, in addition to the above-described information elements, an uplink header information element indicating whether an uplink SDAP header is present in uplink data transmitted via the configured DRB, a downlink header information element indicating whether a downlink SDAP header is present in downlink data received via the configured DRB, a default bearer information element indicating whether the configured DRB is a default radio bearer (default DRB), and the like.

Information elements included in the SRB configuration information elements and the DRB configuration information elements and represented by pdcp-Config or PDCP-Config may be information elements used to establish or change the PDCP 306 for the SRB and/or the DRB and related to the configuration of an NR PDCP entity, and may be replaced with PDCP configuration information elements. The information elements related to the configuration of the NR PDCP entity include an information element indicating the size of an uplink sequence number, an information element indicating the size of a downlink sequence number, an information element indicating a profile of header compression (RObust Header Compression (RoHC)), a re-ordering timer information element, and the like.

An information element represented by DRB-ToReleaseList and included in the information elements represented by RadioBearerConfig may include information indicating one or more DRB identities to be released.

In FIG. 15 , an information element represented by RadioResourceConfigDedicated may be an information element used for configuration, change, release, or the like of the radio bearer. An information element represented by SRB-ToAddMod and included in the information elements represented by RadioResourceConfigDedicated may be information indicating a signaling radio bearer (SRB) configuration, and may be replaced with an SRB configuration information element or a signaling radio bearer configuration information element. An information element represented by SRB-ToAddModList may be a list of piece of information indicating SRB configurations. An information element represented by DRB-ToAddMod and included in the information elements represented by RadioResourceConfigDedicated may be information indicating a data radio bearer (DRB) configuration, and may be replaced with a DRB configuration information element or a data radio bearer configuration information element. An information element represented by DRB-ToAddModList may be a list of pieces of information indicating DRB configurations. Note that any or all of the SRB configurations and the DRB configurations may be referred to as radio bearer configurations.

An information element included in the SRB configuration information elements and represented by SRB-Identity is information of SRB identity of an SRB to be added or changed, and may be an identifier that uniquely identifies the SRB at each terminal apparatus. This information element may be replaced with an SRB identity information element, a radio bearer identity information element, or a signaling radio bearer identity information element. An information element represented by SRB-Identity in FIG. 15 may be an information element having a role identical to the role of the information element represented by SRB-Identity in FIG. 14 .

An information element included in the DRB configurations and represented by DRB-Identity may be information of DRB identity of a DRB to be added or changed and may be a DRB identity uniquely identifying, at each terminal apparatus, the DRB. This information element may be replaced with a DRB identity information element, a radio bearer identity information element, or a data radio bearer identity information element. In the example illustrated in FIG. 15 , the DRB Identity has an integer value ranging from 1 to 32. However, the DRB identity may take another value. The information element represented by DRB-Identity in FIG. 15 may be an information element having a role identical to the role of the information element represented by DRB-Identity in FIG. 14 .

An information element included in the DRB configuration information elements and represented by eps-BearerIdentity may be an EPS bearer identity uniquely identifying an EPS bearer at each terminal apparatus. The information element represented by eps-BearerIdentity may be referred to as an EPS bearer identity information element. In the example illustrated in FIG. 15 , the EPS bearer Identity has an integer value ranging from 1 to 15. However, the EPS bearer identity may take another value. The information element represented by eps-BearerIdentity in FIG. 15 may be an information element having a role identical to the role of the information element represented by eps-BearerIdentity in FIG. 14 . At each terminal apparatus, the EPS bearer identities may correspond to the DRB identities on a one-to-one basis.

An information element included in the SRB configuration information elements and the DRB configuration information elements and represented by pdcp-Config or PDCP-Config may be an information element related to the configuration of an E-UTRA PDCP entity and used to establish or change the PDCP 206 for the SRB and/or for the DRB, and may be replaced with a PDCP configuration information element. The information elements related to the configuration of the E-UTRA PDCP entity may include an information element indicating the size of the sequence number, an information element indicating the profile of header compression (RObust Header Compression (RoHC)), a re-ordering timer information element, and the like.

Additionally, some or all of the information elements illustrated in FIG. 14 or FIG. 15 may be optional. In other words, the information elements illustrated in FIG. 14 or FIG. 15 may be included in a message related to the reconfiguration of RRC connection depending on requirements or conditions. In addition, the message related to the reconfiguration of RRC connection may include an information element meaning that a full configuration is to be applied, in addition to an information element related to the configuration of the radio bearer. The information element meaning that the full configuration is to be applied may be represented by an information element name such as fullConfig, and true, enable, or the like may be used to indicate application of the full configuration.

An information element represented by DRB-ToReleaseList and included in the information elements represented by RadioResourceConfigDedicated may include information indicating one or more DRB identities to be released.

In the following description, the eNB 102 and/or the gNB 108 is simply referred to as a base station apparatus, and the UE 122 is also simply referred to as a terminal apparatus.

In a case that RRC connection is established, in a case that the RRC connection is re-established, or in a case of handover, one serving cell provides mobility information for the NAS. In a case that the RRC connection is re-established or in a case of handover, one serving cell provides a security input. The serving cell is referenced as a primary cell (PCell). Additionally, depending on the capability of the terminal apparatus, one or multiple serving cells (secondary cells, SCells) may be additionally configured together with the primary cell.

A set of serving cells including two subsets may be configured for the terminal apparatus. The two subsets may include a cell group (master cell group) including one or multiple serving cells including the primary cell (PCell), and one or multiple cell groups (secondary cell groups) each including one or multiple serving cells including a primary secondary cell (PSCell) and no primary cell. The primary secondary cell may be a cell configured with a PUCCH resource.

An example of operation related to radio link failure (RLF) by an RRC connected terminal apparatus will be described.

The terminal apparatus uses broadcast information and user-specific RRC messages to acquire, from a serving base station apparatus, information such as values (t310 and t313) of timers (e.g., T310 and T313) for detection of physical layer problems of the serving cell, N310 and N313 corresponding to thresholds for the number of detections of out-of-sync (OoS), and N311 and N314 corresponding to thresholds for the number of detections of in-sync (IS). Default values may be configured for the values of the timers and the threads for the numbers of times. The names of the timers may vary between the EUTRA and the NR.

For radio link monitoring, in a case of estimating that the radio link quality of the serving cell is worse than a specific threshold (Qout) over a specific period of time (e.g., TEvaluate_Qout=200 ms), based on, for example, information such as the received power of a reference signal received and/or the received power of the synchronization signal and/or the error rate of a packet, a physical layer processing unit of the terminal apparatus notifies “out-of-sync” to an RRC layer processing unit corresponding to an upper layer. In a case of estimating that the radio link quality of the serving cell exceeds a specific threshold (Qin) over a specific period of time (e.g., TEvaluate_Qin=100 ms), based on, for example, information such as the received power of the reference signal received and/or the received power of the synchronization signal and/or the error rate of the packet, the physical layer processing unit notifies the RRC layer processing unit corresponding to an upper layer of “in-sync.” Note that the physical layer processing unit may notify the upper layer of out-of-sync or in-sync at specific intervals (e.g., TReport_sync=10 ms) or more.

In this regard, for example, the threshold Qout may be defined as a level at which the downlink radio link fails to be reliably received and further the block error rate of transmission of a hypothetical downlink control channel (PDCCH) based on a predefined parameter is a first specific rate. For example, the threshold Qin may be defined as a level at which the downlink radio link quality can be received significantly more reliably than in the state of Qout and further the block error rate of transmission of the hypothetical downlink control channel based on the predefined parameter is a second specific rate. Multiple block error rates (levels of the threshold Qout and the threshold Qin) may be defined based on the frequency and subcarrier spacing used, the type of service, and the like. The first specific rate and/or the second specific rate may be a predefined value defined in the specifications. The first specific rate and/or the second specific rate may be a value notified or broadcast from the base station apparatus to the terminal apparatus.

The terminal apparatus may monitor the radio link by using a certain type of reference signal (e.g., cell-specific reference signal (CRS)) in the serving cell (e.g., the PCell and/or PSCell). The terminal apparatus may receive, from the base station apparatus, a configuration indicating which reference signal is used for radio link monitoring in the serving cell (e.g., the PCell and/or PSCell) (radio link monitoring configuration: RadioLinkMonitoringConfig), and monitor the radio link by using one or multiple reference signals configured (referred to here as RLM-RSs). The terminal apparatus may monitor the radio link by using any other signal. The physical layer processing unit of the terminal apparatus may notify the upper layer of in-sync in a case that conditions for in-sync are satisfied in the serving cell (e.g., the PCell and/or the PSCell).

The radio link monitoring configuration may include information indicating the purpose of monitoring and identifier information indicating the reference signal. For example, the purpose of monitoring may include the purpose of monitoring radio link failure, the purpose of monitoring beam failure, both of the purposes, and the like. For example, the identifier information indicating the reference signal may include information indicating the identifier (SSB-Index) of a synchronization signal block (SSB) of the cell. That is, the reference signal may include the synchronization signal. For example, the identifier information indicating the reference signal may include information indicating an identifier linked to a channel state information reference signal (CSI-RS) configured for the terminal apparatus.

In the primary cell, in a case that out-of-sync notified from the physical layer processing unit is continuously received a predefined number of times (N310), the RRC layer processing unit of the terminal apparatus may start or restart the timer (T310). In response to a predefined number of (N311) continuous receptions of in-sync, the RRC layer processing unit of the terminal apparatus may stop the timer (T310). The RRC layer processing unit of the terminal apparatus may perform transition to an idle state or an RRC connection re-establishment procedure in a case that the timer (T310) expires. For example, the operation of the terminal apparatus may vary depending on an establishment state of AS Security. In a case that AS Security has not been established, the terminal apparatus transitions to the RRC IDLE state, and in a case that the AS Security has been established, the terminal apparatus may perform a procedure for re-establishing RRC connection (Re-establishment). An additional condition for determining that the timer T310 is to be started or restarted may be that none of the timer T300, the timer T301, the timer T304, and the timer T311 are running.

FIG. 9 illustrates an example of the conditions for start, stop, and expiry of each of the timers of the EUTRA. Note that similar conditions may also be applied in the NR, though the timer name and/or the message name may differ in the NR.

In the primary secondary cell, in a case that out-of-sync notified from the physical layer processing unit is continuously received a predefined number of times (N313), the RRC layer processing unit of the terminal apparatus may start or restart the timer (T313). In a case that in-sync is continuously received a predefined number of times (N314), the RRC layer processing unit of the terminal apparatus may stop the timer (T313). In a case that the timer expires (T313), the RRC layer processing unit of the terminal apparatus may perform an SCG failure information procedure for notifying the network of SCG failure.

In the SpCell (the PCell in the MCG and the PSCell in the SCG), in a case that out-of-sync notified from the physical layer processing unit is continuously received a predefined number of times (N310) in each SpCell, the RRC layer processing unit of the terminal apparatus may start or restart the timer (T310) of the SpCell. In a case that in-sync is continuously received a predefined number of times (N311) in each SpCell, the RRC layer processing unit of the terminal apparatus may stop the timer (T310) for the SpCell. The RRC layer processing unit of the terminal apparatus may perform transition to the idle state or the RRC connection re-establishment procedure in a case that the SpCell is a PCell in a case that the timer (T310) for each SpCell expires. In a case that the SpCell is the PSCell, the SCG failure information procedure may be performed to notify the network of the SCG failure.

The above description is an example of a case in which discontinuous reception (DRX) is not configured for the terminal apparatus. With the DRX configured for the terminal apparatus, the RRC layer processing unit of the terminal apparatus may configure for the physical layer processing unit the period of time for measuring radio link quality and the intervals of notifications to the upper layer such that the period of time and the intervals have values different from those in the case that the DRX is not configured. Note that, even with the DRX configured, in a case that the above-described timer (T310, T313) is running, the period of time when radio link quality is measured for estimation of in-sync and the intervals of notifications to the upper layer may have values identical to those used in a case that the DRX is not configured.

For example, in order to detect an early physical layer problem, the RRC layer processing unit of the terminal apparatus may start the timer (T314) in a case that early out-of-sync notified from the physical layer processing unit is continuously received a predefined number of times (N310). In a case that in-sync is continuously received a predefined number of times (N311) while the T314 is running, the RRC layer processing unit of the terminal apparatus may stop the timer (T314).

For example, in order to detect early improvement of the physical layer, the RRC layer processing unit of the terminal apparatus may start the timer (T315) in a case that early in-sync notified from the physical layer processing unit is continuously received a predefined number of times (N311). In a case that in-sync is continuously received a predefined number of times (N311) while the T315 is running, the RRC layer processing unit of the terminal apparatus may stop the timer (T315).

For example, in a case that measurement is reported to the base station apparatus and that performance of first measurement is configured in measurement configurations (e.g., the measurement is performed using the timer T312), the timer T312 is started in a case that the timer T310 is running, while the timer T312 is not running. The RRC layer processing unit of the terminal apparatus may stop the timer (T312) in a case that in-sync is continuously received a predefined number of times (N311).

The RLM-RS described above may be undefined in a case that the RLM-RS is not explicitly or implicitly configured by the network. In other words, the terminal apparatus need not monitor the radio link in a case that no RLM-RS is configured by the network (for example, the base station apparatus).

The RLM-RS is a reference signal used in monitoring the radio link, and multiple RLM-RSs may be configured for the terminal apparatus. A resource for one RLM-RS may be a resource for one SS block or one CSI-RS (or port).

Radio link monitoring using the CRS may be performed in an EUTRA cell, and radio link monitoring using the RLM-RS may be performed in an NR cell, but no such limitation is intended.

Detection of radio link failure based on radio link monitoring will be described.

The terminal apparatus determines that radio link failure has been detected in the MCG in a case that the timer T310 expires or the timer T312 expires, or in a case that a random access problem is notified from the MAC layer of the MCG while none of the multiple specific timers are running, in a case that the RLC layer of the MCG has notified the terminal apparatus that the number of retransmissions of the SRB or the DRB has reached the maximum number of retransmissions. The specific timers do not include the timer T310 or the timer T312.

The upper layer (in this regard, the RRC entity) may be notified of the random access problem from the MAC entity of the cell group including an SpCell in a case that at the MAC entity, the number of retransmissions of a random access preamble has reached a predefined number and that the random access preamble is transmitted in the SpCell.

In response to determining that radio link failure is detected in the MCG, the terminal apparatus stores various information as radio link failure information. In a case that the security of the AS has not been activated, processing for leaving RRC_CONNECTED is initiated with “other” configured as the reason for release. In a case that the AS security has been activated, the RRC connection re-establishment procedure is initiated.

In a case that the timer T313 expires, in a case that a random access problem is notified from the MAC layer of the SCG, or in a case that the RLC layer of the SCG has notified the terminal apparatus that the number of retransmissions has reached the maximum number of retransmissions, the terminal apparatus determines that radio link failure has been detected in the SCG, and initiates processing for reporting, to the base station apparatus, information related to the SCG radio link failure.

In a case that the timer T314 expires, the terminal apparatus determines that an “early out-of-sync” event has been detected and initiates processing for reporting related information to the base station apparatus.

In a case that the timer T315 expires, the terminal apparatus determines that an “early in-sync” event has been detected, and initiates processing for reporting related information to the base station apparatus.

The RRC connection re-establishment procedure will be described.

The purpose of the RRC connection re-establishment procedure is to re-establish RRC connection, and the procedure may involve a procedure for resuming SRB1, reactivation of security, and configuration of only the PCell.

The RRC connection re-establishment procedure may be initiated in a case that any of conditions (A) to (E) below is satisfied:

(A) in a case that radio link failure in the MCG is detected;

(B) in a case that handover fails (in the NR, in a case that Reconfiguration With Sync in the MCG fails);

(C) in a case that mobility to another RAT fails;

(D) in a case that failure in integrity check related to SRB1 or SRB2 is notified from the lower layer;

(E) in a case that RRC connection reconfiguration fails.

In a case that the RRC connection re-establishment procedure is initiated, the terminal apparatus performs some or all of steps of processing (A) to (K) below:

(A) in a case that the timer T310 is running, stop the timer T310;

(B) in a case that the timer T312 is running, stop the timer T312;

(C) in a case that the timer T313 is running, stop the timer T313;

(D) in a case that the timer T314 is running, stop the timer T314;

(E) start the timer T311;

(F) suspend all the RBs other than SRB0;

(G) reset the MAC;

(H) in a case that the SCell of the MCG is configured, release the SCell of the MCG;

(I) apply the default physical channel configuration;

(J) apply a default MAC main configuration to the MCG;

(K) perform the cell selection procedure.

In a case that an optimal cell of an identical RAT is selected by the cell selection procedure, the terminal apparatus performs the following processing.

In a case that the terminal apparatus is connected to the 5GC and that the cell selected can be connected only to the EPC or in a case that the terminal apparatus is connected to the EPC and that the cell selected can be connected only to the 5GC, the terminal apparatus performs an action for leaving RRC_CONNECTED with “RRC connection failure” configured as a reason for release. Otherwise, the terminal apparatus stops the timer T311, starts the timer T301, and initiates transmission of an RRC connection re-establishment request (ReestablishmentRequest) message.

In a case that the timer T311 expires, the terminal apparatus performs the action for leaving RRC_CONNECTED with “RRC connection failure” configured as a reason for failure.

In a case that the timer T301 expires or in a case that the cell selected is no longer the optimal cell in terms of cell selection criterion, the terminal apparatus performs the action for leaving RRC_CONNECTED with “RRC connection failure” configured as a reason for failure.

Handover will be described.

An example of processing related to handover in the EUTRA between the same RATs (i.e., between the EUTRAs) will be described using FIG. 7 . The description using FIG. 7 is an example, and the processing may partly be omitted or include another processing. Alternatively, another processing may be performed as processing related to handover.

In FIG. 7 , a base station apparatus used as a handover source (source eNB) configures the terminal apparatus with measurement of neighbor cells (step S701).

The terminal apparatus performs the measurement configured by the Source eNB, and reports measurement results to the Source eNB, based on reporting conditions (step S702).

The Source eNB determines handoff of the terminal apparatus, based on information such as the measurement results reported (step S703).

The Source eNB issues a handover request message including information required to prepare for the handover, to a base station apparatus used as a handover destination (Target eNB) (step S704).

Admission control may be performed in the Target eNB. The Target eNB configures the required resources. (step S705).

The Target eNB sends a HANDOVER REQUEST ACKNOWLEDGE message to the Source eNB (step S706). The HANDOVER REQUEST ACKNOWLEDGE message includes, as an RRC message for performance of handover, a container transmitted transparently to the terminal apparatus. The container may include some or all of a new C-RNTI, a security algorithm identity of the Target eNB for a selected security algorithm, a preamble of a dedicated random access channel (random access preamble), system information of the target cell, and the like.

The Source eNB may send the terminal apparatus a first RRC connection reconfiguration message (RRCConnectionReconfiguration message) including a container (mobility control information (mobilityControlInfo)) information element (IE) received from the target eNB (step S707).

Note that in a case that make before break-handover (Make-Before-Break HO (MBB-HO)) is configured by the first RRC connection reconfiguration message, the terminal apparatus receives the first RRC connection reconfiguration message and then maintains connection with the Source eNB at least until the Target eNB performs the first uplink transmission. Note that the make before break-handover may be selected from multiple configurations. For example, configuration of true in a field makeBeforeBreak-r14 included in a mobilityControlInfo information element already specified may allow determination that make before break-handover is configured. For example, in a case that makeBeforeBreak-r16 to be newly defined is included in the field of the mobilityControlInfo information element and that true is configured in makeBeforeBreak-r16, determination that make before break-handover is configured. The field makeBeforeBreak-r16 may include, as values, information elements including various configurations.

The Source eNB sends the Target eNB an SN STATUS TRANSFER message for communicating (Conveying) the reception state of the sequence number of the uplink PDCP and the transmission state of the sequence number of the downlink PDCP (step S708).

In a case that RACH-less handover is not configured by the first RRC connection reconfiguration message, the terminal apparatus performs synchronization with the Target eNB and uses a random access channel to access the cell used as a target. At this time, in a case that a dedicated random access preamble is indicated by the first RRC connection reconfiguration message, the terminal apparatus performs a contention-free random access procedure. In a case that no dedicated random access preamble is indicated, the terminal apparatus performs a contention-based random access procedure. In a case that RACH-less handover is configured by the first RRC connection reconfiguration message, the terminal apparatus performs synchronization with the Target eNB (step S709).

In a case that no RACH-less handover is configured by the first RRC connection reconfiguration message, the Target eNB returns information of uplink allocation and timing advance to the terminal apparatus (step S710).

In a case that RACH-less handover is configured by the first RRC connection reconfiguration message and that periodic pre-allocated uplink grant has failed to be acquired by the first RRC connection reconfiguration message, the terminal apparatus receives the uplink grant by the PDCCH of the target cell. The terminal apparatus uses the first available uplink grant after synchronization with the target cell (step S710 a).

With RACH-less handover not configured, in a case that the terminal apparatus successfully accesses the target cell, the terminal apparatus sends an RRC connection reconfiguration complete message (RRCConnectionReconfigurationComplete message) to the Target eNB to confirm handover. This RRC connection reconfiguration complete message indicates completion of a handover procedure of the terminal apparatus. The RRC connection reconfiguration complete message includes a C-RNTI, and the Target eNB verifies the C-RNTI of the RRC connection reconfiguration complete message received.

In a case that RACH-less handover is configured and that the terminal apparatus receives the uplink grant, the terminal apparatus sends the RRC connection reconfiguration complete message (RRCConnectionReconfigurationComplete message) to the Target eNB to confirm handover. The RRC connection reconfiguration complete message includes a C-RNTI, and the Target eNB verifies the C-RNTI of the RRC connection reconfiguration complete message received. In a case that the terminal apparatus receives a UE contention resolution identity MAC control element from the Target eNB, the handover procedure of the terminal apparatus completes (step S711).

The Target eNB sends a PATH SWITCH REQUEST message to the MME to notify the MME that the terminal apparatus has changed the cell (step S712).

The MME sends a MODIFY BEARER REQUEST message to a serving gateway (S-GW) (step S713).

The S-GW switches a downlink data path to the target side. The S-GW sends one or multiple end marker packets to the Source eNB and releases user plane resources to the Source eNB (step S714).

The S-GW sends a MODIFY BEARER RESPONSE message to the MME (step S715).

The MME checks the path switch request by using the PATH SWITCH REQUEST ACKNOWLEDGE message (step S716).

The Target eNB sends a UE CONTEXT RELEASE message to the Source eNB to indicate the success of handover, triggering release of resources by the Source eNB. The Target eNB may send this message after receiving the path switch request acknowledge message (step S717).

In response to receiving a UE context release message, the Source eNB can release resources associated with radio and a C-plane related to the UE context. Data forwarding in performance may be continued (step S718).

In a case that the timer T304 expires, the terminal apparatus performs some or all of steps of processing (A) to (D) below:

(A) consider the configuration of the dedicated random access channel to be unavailable, the dedicated random access channel being configured by the first RRC connection reconfiguration message;

(B) change the configurations for the terminal apparatus back to the configurations used in the PCell of the handover source, except for the configuration of the dedicated physical channel, the main configuration of the MAC layer, and the configuration of a semi-persistent schedule;

(C) store related information as handover failure information;

(D) initiate the RRC connection re-establishment procedure and terminate the RRC connection reconfiguration procedure.

Details of processing performed by the terminal apparatus in response to receiving the first RRC connection reconfiguration message will be described. The first RRC connection reconfiguration message may include a mobility control information (mobilityControlInfo) information element. The mobilityControlInfo information element includes parameters related to the mobility of network control from another RAT to the EUTRA or within the EUTRA (e.g., information of the identifier of the target cell and a carrier frequency).

In a case that the terminal apparatus receives the RRC connection reconfiguration message including the mobilityControlInfo information element (first RRC connection reconfiguration message) and can satisfy the configuration in the message, the terminal apparatus performs some or all of steps of processing (A) to (G) below:

(A) in a case that the timer T310 is running, stop the timer T310;

(B) in a case that the timer T312 is running, stop the timer T312;

(C) in a case that the timer T314 is running, stop the timer T314;

(D) start the timer T304 at a value (t304) included in the mobilityControlInfo information element;

(E) in a case that the information of the carrier frequency is included, determine that the frequency is the frequency of the target cell, and in a case that the information of the carrier frequency is not included, determine that the frequency of the source PCell is the frequency of the target cell;

(F) in a case that a timer for which access is restricted is running, stop the timer;

(G) initiate downlink synchronization in the target cell.

An example of processing related to handover between the same RATs (i.e., between the NRs) in NR will be described using FIG. 8 . The description using FIG. 8 is an example, and the processing may partly be omitted or include another processing. Alternatively, another processing may be performed as processing related to handover.

In FIG. 8 , the base station apparatus used as a handover source (Source gNB) configures the terminal apparatus with measurement of neighbor cells, and the terminal apparatus performs the measurement configured by the Source gNB and reports measurement results to the Source gNB (step S801).

The Source gNB determines handoff of the terminal apparatus, based on information such as the measurement results reported (step S802).

The Source gNB issues a handover request message including information required to prepare for handover, to a base station apparatus used as a handover destination (Target gNB) (step S803).

Admission control may be performed in the Target gNB (step S804).

The Target gNB prepares for handover and sends the Source gNB the HANDOVER REQUEST ACKNOWLEDGE message to the Source eNB (step S805). The HANDOVER REQUEST ACKNOWLEDGE message includes, as an RRC message for performance of handover, a container transmitted transparently to the terminal apparatus.

The Source gNB sends the terminal apparatus the container received from the Target gNB (the first RRC reconfiguration message (RRCReconfiguration message)) (step S806). The RRC reconfiguration message may include some or all of the identifier of the target cell, a new C-RNTI, the security algorithm identity of the Target gNB for a selected security algorithm, a set of resources for the dedicated random access channel, the configuration of a UE-specific CSI-RS, common random access channel resources, and the system information of the target cell.

Note that in a case that make before break-handover (Make-Before-Break HO (MBB-HO)) is configured by the first RRC reconfiguration message, the terminal apparatus may maintain connection with the Source gNB from reception of the first RRC reconfiguration message at least until the Target gNB performs the first uplink transmission.

The Source eNB sends the Target gNB the SN STATUS TRANSFER message for communicating (conveying) the reception state of the sequence number of the uplink PDCP and the transmission state of the sequence number of the downlink PDCP (step S807).

In a case that no RACH-less handover is configured by the first RRC reconfiguration message, the terminal apparatus performs synchronization with the Target eNB and uses the random access channel to access the cell used as a target. At this time, in a case that a dedicated random access preamble is indicated by the first RRC reconfiguration message, the terminal apparatus may perform the contention-free random access procedure. In a case that no dedicated random access preamble is indicated by the first RRC reconfiguration message, the terminal apparatus may perform the contention-based random access procedure. In a case that RACH-less handover is configured by the first RRC reconfiguration message, the terminal apparatus performs synchronization with the Target gNB.

In a case that no RACH-less handover is configured by the first RRC reconfiguration message, the Target gNB may return information of uplink allocation and timing advance to the terminal apparatus.

In a case that RACH-less handover is configured by the first RRC reconfiguration message and that periodic pre-allocated uplink grant has failed to be acquired by the first RRC reconfiguration message, the terminal apparatus receives the uplink grant by the PDCCH of the target cell. The terminal apparatus uses the first available uplink grant after synchronization with the target cell.

With RACH-less handover not configured, in a case that the terminal apparatus successfully accesses the target cell, the terminal apparatus may send the RRC reconfiguration complete message (RRCReconfigurationComplete message) to the Target gNB to confirm handover. The RRC reconfiguration complete message may indicate completion of the handover procedure of the terminal apparatus. The RRC reconfiguration complete message includes the C-RNTI, and the Target gNB may verify the C-RNTI of the RRC reconfiguration complete message received.

In a case that the RACH-less handover is configured and that the terminal apparatus receives the uplink grant, the terminal apparatus may send an RRC reconfiguration complete (RRCReconfigurationComplete) message to the Target gNB to confirm handover. The RRC reconfiguration complete message includes the C-RNTI, and the Target gNB may verify the C-RNTI of the RRC reconfiguration complete message received. In a case that the terminal apparatus receives the UE contention resolution identity MAC control element from the Target gNB, the handover procedure of the terminal apparatus may complete (step S808).

The Target eNB sends the PATH SWITCH REQUEST message to the AMF to cause the 5GC to switch the downlink data path to the Target gNB to establish an NG-C interface instance for the Target gNB (step S809).

The 5GC switches the downlink data path to the Target gNB. UPF sends one or multiple end marker packets to the Source eNB to release the user plane resources for the Source gNB (step S810).

The AMF checks the path switch request by using the PATH SWITCH REQUEST ACKNOWLEDGE message (step S811).

The Target gNB sends the UE CONTEXT RELEASE message to the Source eNB to indicate the success of handover, triggering release of resources by the Source gNB. The Target gNB may send this message after receiving the path switch request acknowledge message from the AMF. In response to receiving the UE context release message, the Source gNB can release resources associated with the radio and C-plane related to the UE context. The data forwarding in performance may be continued (step S812).

In a case that the timer T304 expires, the terminal apparatus performs some or all of steps of processing (A) to (D) below:

(A) in a case that the timer T304 of the MCG expires, release the configuration of the dedicated random access channel of the MCG configured by the first RRC connection reconfiguration message;

(B) in a case that the timer T304 of the MCG expires, change the configurations for the terminal apparatus back to the configurations used in the PCell of the handover source;

(D) in a case that the timer T304 of the MCG expires, initiate the RRC connection re-establishment procedure;

(E) in a case that the timer T304 of the SCG expires, release the configuration of the dedicated random access channel of the SCG configured by the first RRC connection reconfiguration message;

(E) in a case that the timer T304 of the SCG expires, initiate the procedure for reporting failure in Reconfiguration With Sync in the SCG.

Details of processing performed by the terminal apparatus in response to receiving the first RRC reconfiguration message will be described. The first RRC reconfiguration message may include a Reconfiguration With Sync (reconfigurationWithSync) information element. The reconfigurationWithSync information element may be included in the configuration of the SpCell for each cell group (MCG or SCG) in the RRC reconfiguration message. The reconfigurationWithSync information element includes parameters related to reconfigurationWithSync with the target SpCell (e.g., the configuration of the target SpCell, a new identifier for the terminal apparatus, and the like).

In response to receiving the RRC reconfiguration message including the reconfigurationWithSync information element (first RRC reconfiguration message), the terminal apparatus performs some or all of steps of processing (A) to (E) below:

(A) in a case that security has not been activated, initiate the processing for leaving RRC_CONNECTED with “other” configured as a reason for release. The processing for leaving the RRC_CONNECTED may be processing for heading for the RRC_IDLE;

(B) in a case that the timer T310 of the target SpCell is running, stop the timer T310 of the target SpCell;

(C) start the timer T304 of the target SpCell at a value (t304) included in the reconfigurationWithSync information element;

(D) in a case that the information of the downlink frequency is included, determine that the frequency is the frequency of SSB of the target cell, and in a case that the information of the downlink frequency is not included, determined that the frequency of SSB of the source SpCell is the frequency of SSB of the target cell;

(E) initiate downlink synchronization in the target cell.

As described above, in the EUTRA and/or NR, in a case of being configured with make before break-handover (Make-Before-Break HO (MBB-HO)), the terminal apparatus may maintain connection with the Source eNB or the Source gNB until the Target eNB or the Target gNB performs the first uplink transmission or until any period. At present, the timer T310 is stopped in response to reception of the first RRC connection reconfiguration message or the first RRC reconfiguration message. Thus, in the subsequent Source eNB or the serving cell (source cell) of the Source gNB, the terminal apparatus fails to determine whether the situation is considered to be a radio link failure caused by a physical layer problem. In a case that the timer T304 is running, in the Source eNB or the serving cell (source cell) of the Source gNB, the terminal apparatus fails to determine whether the situation is considered to be radio link failure caused by a random access problem notified from the MAC layer. In the source cell, in a case that the number of retransmissions based on RLC reaches the maximum number, this is considered to be radio link failure, and the RRC connection re-establishment procedure is performed.

Note that, in the make before break-handover (Make-Before-Break HO (MBB-HO)), in order to maintain connection with a Source eNB or a Source gNB until the Target eNB or the Target gNB performs first uplink transmission or until any period, an activated protocol layer may be used in each of the Source side and the Target side. Thus, the make before break-handover (MBB-HO) may be interpreted as a Dual Active Protocol Stack (DAPS) handover. In the DAPS handover, in the PDCP entity, two secrecy keys, and/or two integrity keys, and/or two RoHC protocols for the source and for the target may be configured, two RLC bearers for the source and for the target may be configured, and two MAC entities for the source and for the target may be configured. A part or all of the secrecy keys, the integrity keys, the RoHC protocols, the RLC bearers, and the MAC bearers configured for the source and for the target described above may be simultaneously or alternately used in a case of a handover using the DAPS. In the following, the make before break-handover (MBB-HO) may be interpreted as a DAPS handover.

In the following description, “the make before break-handover is applied” may be “the DAPS handover is applied”. Further, “the make before break-handover (MBB-HO) is configured for the terminal apparatus” may be “the DAPS handover is configured for the terminal apparatus”. Further, “the make before break-handover (MBB-HO) is configured (the DAPS handover is configured) for the terminal apparatus” may be “the MBB-HO (DAPS handover) is applied to any one radio bearer configured for the terminal apparatus” or “the MBB-HO (DAPS handover) is applied to at least one of the radio bearers configured for the terminal apparatus”.

Now, conditional handover will be described. In the NR, conditional handover may be an RRC reconfiguration using an RRC reconfiguration message including an information element (conditional handover configuration) including information included in the Reconfiguration With Sync information element and information indicating a condition for applying the information element (conditional handover condition). In the LTE, conditional handover may be an RRC connection reconfiguration using an RRC connection reconfiguration message including an information element (conditional handover configuration) including information included in the mobility control information element and information indicating a condition for applying the information element (conditional handover condition).

In the NR, the conditional handover configuration may include some or all of configurations (A) to (F) below.

(A) Configuration information of the cell group (CellGroupConfig)

(B) Information indicating whether a full configuration has been provided.

(C) NAS layer message

(D) System information

(E) Measurement configuration

(F) Configuration of the radio bearer

The configuration information of the cell group may include some or all of configurations (1) to (6) below.

(1) Identifier of the cell group

(2) Information of the RLC bearer

(3) Configuration information of MAC layer of the cell group

(4) Configuration information of physical (PHY) layer of the cell group

(5) Configuration information of the SpCell (the information may include the Reconfiguration With Sync information element)

(6) Information of the SCell

The configuration of the radio bearer may include some or all of the configurations (1) to (3) below.

(1) SRB configuration

(2) DRB configuration

(3) Security configuration (for example, information related to an integrity protection algorithm and a ciphering algorithm for the SRB and/or the DRB (securityAlgorithmConfig), information (keyToUse) indicating which key of the master (MCG) and the secondary (SCG) is to be used, and the like)

In the LTE, the conditional handover configuration may include some or all of configurations (A) to (E) below.

(A) Measurement configuration

(B) Mobility control information element

(C) NAS layer message

(D) Radio resource configuration

(E) Security configuration (e.g., information related to the integrity protection algorithm and the ciphering algorithm for the SRB and/or the DRB (SecurityAlgorithmConfig))

The above-described radio resource configuration may include some or all of configurations (1) to (4) below.

(1) SRB information

(2) DRB information

(3) Configuration information of MAC layer of the cell group

(4) Configuration information of physical (PHY) layer of the cell group

In the LTE and/or NR, the conditional handover condition may include some or all of conditions (A) to (D) below.

(A) The cell of the handover destination (target) has become better than the current (source) PCell with an offset

(B) The cell of the handover destination (target) has become better than a certain threshold, and the PCell has become worse than another threshold.

(C) The cell of the handover destination (target) has become better than a certain threshold

(D) No condition (handover is performed immediately)

For comparison under the conditional handover conditions described above, RSRP, RSRQ, and/or RS-SINR may be used as quantities. Which of the quantities is used may be configured by the network. Information indicating which quantity is to be used may be included in the conditional handover condition.

The information element indicating the conditional handover configuration and/or the conditional handover condition may be included as part of the RRC message at the handover source, or may be stored in the container (information element that stores a bit sequence) included in the RRC message.

Various embodiments of the present invention will be described based on the foregoing description. Note that, for each of the steps of processing omitted in the following description, each of the steps of processing described above may be applied.

An example will be described in which MBB-HO is efficiently performed by changing the procedure related to radio link monitoring in MBB-HO.

First, in the primary cell (PCell) corresponding to the SpCell of the MCG, under a specific condition (first condition), regardless of whether the timer T304 is running, the RRC layer processing unit of the UE 122 may start or restart the timer (T310) in a case that out-of-sync notified from the physical layer processing unit is continuously received a predefined number of times (N310). The RRC layer processing unit of the UE 122 may stop the timer (T310) in a case that in-sync is continuously received a predefined number of times (N311). An additional condition for determining that the timer T310 is to be started or restarted may be that none of the timer T300, the timer T301, and the timer T311 are running.

The RRC layer processing unit of the UE 122 determines that radio link failure has been detected in the MCG in response to satisfaction of any of the conditions (A) to (E) below:

(A) in a case that the timer T310 expires;

(B) in a case that the timer T312 expires;

(C) in a case that a notification (indication) of a random access problem is received from the MAC entity of the MCG while none of the timer T300, the timer T301, the timer T304, and the timer T311 are running

(D) in a case that a notification of a random access problem is received from the MAC entity of the MCG while the first condition is satisfied and the timer T304 is running;

(E) in a case that a notification indicating that the number of retransmissions of the SRB or the DRB has reached the maximum number of retransmissions is received from the RLC layer of the MCG.

The first condition may be that makeBeforeBreak-r16 is configured for the UE 122. The configuration of makeBeforeBreak-r16 may correspond to, for example, in a case of the EUTRA, the reception, by the UE 122, of the RRC connection reconfiguration message in which makeBeforeBreak-r16 is included in a field of the mobilityControlInfo information element. The configuration of makeBeforeBreak-r16 may correspond to, for example, in a case of the NR, the reception of the RRC reconfiguration message in which the makeBeforeBreak-r16 is included in a field of the Reconfiguration With Sync information element. The non-configuration of makeBeforeBreak-r16 may correspond to, for example, in a case of the EUTRA, the reception, by the UE 122, of the RRC connection reconfiguration message in which makeBeforeBreak-r16 is not included in any field of the mobilityControlInfo information element. The makeBeforeBreak-r16 not being configured may correspond to, for example, in a case of the EUTRA, the reception, by the UE 122, of the RRC connection reconfiguration message including makeBeforeBreak-r16 having a value of false. The makeBeforeBreak-r16 not being configured may correspond to, for example, in a case of the NR, the reception of the RRC reconfiguration message in which makeBeforeBreak-r16 is not included in any field of the Reconfiguration With Sync information element.

The configuration of makeBeforeBreak-r16 may correspond to, for example, in a case of the EUTRA, the reception, by the UE 122, of the RRC connection reconfiguration message in which makeBeforeBreak-r16 is included in a terminal apparatus-specific radio resource configuration (radioBearerConfigDedicated) information element. The configuration of makeBeforeBreak-r16 may correspond to, for example, in a case of the NR, the reception of the RRC reconfiguration message in which the makeBeforeBreak-r16 is included in a field of the data radio bearer configuration information element.

makeBeforeBreak-r16 may have, for example, an enumerated type value including true, or may have, as a value, an information element including information required for make before break-handover.

The condition (E) described above may be (E2) below.

(E2) In response to reception, from the RLC layer of the MCG, of a notification indicating that the number of retransmissions of the SRB or the DRB has reached the maximum number of retransmissions while none of the timer T300, the timer T301, the timer T304, and the timer T311 are running, or in response to reception, from the RLC layer of the MCG, of a notification indicating that the number of retransmissions of the SRB or the DRB has reached the maximum number of retransmissions, in a case that the first condition is satisfied and while the timer T304 is running.

In response to determining that radio link failure has been detected in the MCG, the UE 122 stores various pieces of information as radio link failure information. In a case that the AS security has not been activated, the processing for leaving RRC_CONNECTED may be initiated with “Other” configured as a reason for release.

In a case that the AS security has been activated and that the first condition is satisfied, part or all of transmission of the SRB and/or DRB in the MCG may be suspended, and the MAC entity of the MCG may be reset.

In a case that the AS security has been activated and that the first condition is not satisfied, the RRC connection re-establishment procedure may be initiated.

The RRC connection re-establishment procedure may be initiated in a case that any of conditions (A) to (E) below is satisfied:

(A) in a case that radio link failure in the MCG is detected while the first condition is not satisfied;

(B) in a case that handover fails (in the NR, in a case that Reconfiguration With Sync in the MCG fails);

(C) in a case that mobility to another RAT fails;

(D) failure in integrity check related to SRB1 or SRB2 is notified from the lower layer;

(E) in a case that RRC connection reconfiguration fails.

In a case that any of the above-described conditions has been satisfied, that the first condition is satisfied, and that the MCG used as a handover source has not detected radio link failure, then the RRC connection re-establishment procedure is not initiated, and the procedure in which the MCG used as a handover source notifies handover failure may be initiated.

In a case that the first condition is that makeBeforeBreak-r16 is configured for the UE 122, makeBeforeBreak-r16 configured may be released in a case that the timer T304 expires or that the procedure in which the MCG used as a handover source notifies handover failure is initiated.

In response to initiation of the RRC connection re-establishment procedure, the UE 122 performs some or all of steps of processing (A) to (J) below:

(A) in a case that the timer T310 is running, stop the timer T310;

(B) in a case that the timer T312 is running, stop the timer T312;

(C) in a case that the timer T313 is running, stop the timer T313;

(C) in a case that the timer T314 is running, stop the timer T314;

(D) start the timer T311;

(E) suspend all the RBs other than SRB0;

(F) reset the MAC;

(G) in a case that the SCell of the MCG is configured, release the SCell of the MCG;

(H) apply the default physical channel configuration;

(I) apply the default main configuration of the MAC to the MCG;

(J) perform the cell selection procedure.

Next, a case has been studied in which, in the handover processing, after transmitting the RRC connection reconfiguration complete message or the RRC reconfiguration complete message to the target cell, the UE 122 transmits and/or receives data via a cell group of both the MCG resulting from handover (also referred to as the Target MCG or Current MCG) and the MCG used as a handover source (Source MCG) (a case of operation in a Dual protocol stack). An example of the processing in that case will be described. Note that the following processing is not limited to the case of the Dual protocol stack, and may be applied in other cases.

First, in the primary cell used as the SpCell of the Source MCG, under a particular condition (first condition), the RRC layer processing unit of the UE 122 may start or restart the timer (T310) for the Source MCG in a case that out-of-sync notified from the physical layer processing unit of the Source MCG is received a predefined number of times (N310), regardless of whether the timer T304 for the Source MCG is running. The RRC layer processing unit of the UE 122 may stop the timer (T310) in a case that the RRC layer processing unit of the UE 122 continuously receives in-sync a predefined number of times (N311 times) from the physical layer processing unit of the Source MCG. An additional condition for determining to start or restart the timer T310 may be that none of the Source MCG timer T300, the Source MCG timer T301, and the Source MCG timer T311 are running.

In a case that any of conditions (A) to (E) below is satisfied, the RRC layer processing unit of the UE 122 determines that radio link failure has been detected in the Source MCG.

(A) in a case that the Source MCG timer T310 expires;

(B) in a case that the Source MCG timer T312 expires;

(C) in a case that a notification (indication) of a random access problem is received from the MAC entity of the Source MCG while none of the timer T300, the timer T301, the timer T304, and the timer T311 for the Source MCG are running;

(D) in a case that notification of a random access problem is received from the MAC entity of the Source MCG while the first condition is satisfied and Source MCG timer T304 is running;

(E) in a case that a notification indicating that the number of retransmissions of the SRB or DRB has reached the maximum number of retransmissions is received from the RLC layer of the Source MCG.

The first condition may be that makeBeforeBreak-r16 is configured for the UE 122.

The first condition may be that either makeBeforeBreak-r14 or makeBeforeBreak-r16 is configured for the UE 122.

The condition (E) described above may be (E2) below.

(E2) in a case that a notification indicating that the number of retransmissions of the SRB or DRB has reached the maximum number of retransmissions is received from the RLC layer of the Source MCG while the none of the timer T300, the timer T301, the timer T304, and the timer T311 for the Source MCG are running, or a notification indicating that the number of retransmissions of the SRB or DRB has reached the maximum number of retransmissions is received from the RLC layer of the Source MCG while the first condition is satisfied and the timer T304 is running.

In response to determining that radio link failure has been detected in the Source MCG, the UE 122 may suspend the transmission of some or all of the SRBs and/or DRBs of the Source MCG and reset the MAC entity of the Source MCG.

In response to configuration of makeBeforeBreak-r16 in the Current MCG, the UE 122 may consider the MCG to be the Source MCG.

In response to allocation of the first uplink grant in the handover destination cell by the PDCCH, the UE 122 may consider the handover source MCG to be the Source MCG.

In response to transmission of the RRC reconfiguration complete message, the UE 122 may consider the handover source MCG to be the Source MCG.

In response to reception of the UE contention resolution identity MAC control element from the Target gNB, the UE 122 may consider the handover source MCG to be the Source MCG.

In a case that the Source MCG is already present in the Current MCG at the time of configuration of makeBeforeBreak-r16, the UE 122 may release the MCG and consider the Current MCG to be a new Source MCG.

In this way, by distinguishing the processing for detecting radio link failure in the Source MCG from the processing for detecting radio link failure in the Current MCG, unnecessary re-establishment processing in MBB-HO can be prevented, allowing efficient mobility to be achieved.

An example of the operation of MBB-HO will be described. In this regard, an example will be described in which in the NR, the RRC reconfiguration message is used that includes CellGroupConfig including the Reconfiguration With Sync information element. Note that the description of processing below includes description of reception of an information element but that this means that the information element is included in the RRC reconfiguration message triggering the processing unless otherwise indicated. The information element used in processing may be associated with the information element used in NPL 10 unless otherwise indicated.

The terminal apparatus performs processing A, based on a CellGroupConfig information element received. The terminal apparatus performs processing L, based on a masterKeyUpdate information element received. The terminal apparatus performs processing I, based on a RadioBearerConfig information element received.

Note that each item of each of the processing described below is assigned an indent and a code. For example, processing A, processing B, processing C, and processing H are respectively interpreted to constitute flows illustrated in FIG. 16 , FIG. 17 , FIG. 18 , and FIG. 19 , and processing other than the above is similarly interpreted.

Processing A

The following processing is performed based on the CellGroupConfig information element received:

(A-0) in a case that CellGroupConfig includes configuration information (spCellConfig information elements) of the SpCell including Reconfiguration With Sync information and the Reconfiguration With Sync information includes information (e.g., MakeBeforeBreak-r16) indicating that the RRC reconfiguration is MBB-HO:

-   -   (A-0-1) replicate the configuration of the current terminal         apparatus (the configuration of the source) as a target         configuration, and subsequent processing may be performed on the         target configuration replicated unless otherwise indicated. For         example, the “configuration of the current terminal apparatus”         for processing may be, for MBB-HO, considered to be the “target         configuration of the current terminal apparatus.” In addition,         for example, the configuration replicated includes some or all         of (1) the configuration related to the bearer (for example, the         configuration related to the SRB, the configuration related to         the DRB, and the like), (2) the configurations of the cell group         (e.g., the configuration of the SpCell, the configuration of the         SCell, the configuration of each entity, and the like), (3)         variables (measurement configuration (VarMeasConfig), a         measurement result (VarMeasReportList), a timer, a counter,         etc.) held inside the terminal apparatus, and (4) the         configuration related to security (e.g., keys). The         configuration of the bearer replicated may exclude a         configuration related to the SRB. Specifically, for the DRB,         both the source configuration and the target configuration may         be managed, and for the SRB, with the replication of the         configuration being avoided, the source configuration may be         switched to the target configuration. Information enabling         determination of whether to replicate the SRB configuration may         be included in the RRC reconfiguration message including         Reconfiguration With Sync. For example, the above-described         information may be included in MakeBeforeBreak-r16;

(A-1) in a case that CellGroupConfig includes configuration information (spCellConfig information elements) of the SpCell including Reconfiguration With Sync information:

-   -   (A-1-1) perform the processing B described below;     -   (A-1-2) in a case of a suspended state, resume all radio bearers         suspended and resume the transmission on the SCG for all of the         radio bearers;

(A-2) in a case that CellGroupConfig includes a list of RLC bearers to be released (rlc-BearerToReleaseList information elements):

-   -   (A-2-1) perform the processing C described below;

(A-3) in a case that CellGroupConfig includes a list of RLC bearers to be added and/or changed (rlc-BearerToAddModList information elements):

-   -   (A-3-1) perform the processing D described below;

(A-4) in a case that CellGroupConfig includes MAC configurations for the cell group (mac-CellGroupConfig information elements):

-   -   (A-4-1) configure the MAC entity of the cell group by the         processing E described below. Note that in the embodiments of         the present invention, the terminal apparatus performing         “configuration” using the information elements included in the         RRC message may refer to applying, to the configuration of the         terminal apparatus, the information included in the information         elements;

(A-5) in a case that CellGroupConfig includes a list of SCells to be released (sCellToReleaseList information elements):

-   -   (A-5-1) perform release of the SCell by the processing F         described below;

(A-6) in a case that CellGroupConfig includes configuration information (spCellConfig information elements) of the SpCell:

-   -   (A-6-1) configure the SpCell by the processing G described         below;

(A-7) in a case that CellGroupConfig includes a list of SCells to be added and/or changed (sCellToAddModList information elements):

-   -   (A-7-1) add and/or change the SCell by the processing H         described below.

Processing B

The following processing is performed:

(B-1) in a case that the AS security has not been activated, perform processing for transitioning to RRC_IDLE and terminate the processing B;

(B-2) in a case that the timer T310 for the corresponding SpCell is running, stop the timer T310;

(B-3) start the timer T304 fore corresponding SpCell using the timer value of t304 included in Reconfiguration With Sync;

(B-4) in a case that frequency information (frequencyInfoDL) is included:

-   -   (B-4-1) consider the target SpCell to be a cell having an SSB         frequency indicated by frequencyInfoDL and having a physical         cell identity indicated by the physical cell identity         information (physCellId) included in Reconfiguration With Sync;

(B-5) Otherwise:

-   -   (B-5-1) consider the target SpCell to be a cell having the SSB         frequency of the source SpCell and having a physical cell         identity indicated by the physical cell identity information         (physCellId) included in Reconfiguration With Sync;

(B-6) initiate downlink synchronization in the target SpCell;

(B-7) apply predefined BCCH configurations;

(B-8) acquire a master information block (MIB) being one of pieces of broadcast information as necessary;

(B-9) in a case that Reconfiguration With Sync includes information indicating MBB-HO:

-   -   (B-9-1) in a case that no MAC entity is present in the cell         group used as a target:         -   (B-9-1-1) generate a MAC entity of the cell group used as a             target (also simply referred to as the target MAC entity);     -   (B-9-2) apply predefined (default) MAC cell group configurations         to the target MAC entity;     -   (B-9-3) consider the SCell of the target cell group to be in a         deactivated state in a case that this configuration is provided;     -   (B-9-4) apply the value of newUE-Identity as the C-RNTI of the         target cell group;

(B-10) Otherwise:

-   -   (B-10-1) reset the MAC entity of the cell group;     -   (B-10-2) consider the SCell of the target cell group to be in         the deactivated state in a case that this configuration is         provided;     -   (B-10-3) apply the value of newUE-Identity as the C-RNTI of the         cell group;

(B-11) configure the lower layer based on the configuration of the SpCell (spCellConfigCommon) included in Reconfiguration With Sync;

(B-12) configure the lower layer based on other information included in Reconfiguration With Sync as necessary.

Processing C

The following process is performed:

(C-1a) for each of the values of logical channel identities (logicalChannelIdentity) that are part of the configuration of the current terminal apparatus and that are included in rlc-BearerToReleaseList: or

(C-1b) for each of the values of the logical channel identities to be released as a result of the release of the SCG:

-   -   (C-1-1) release the corresponding logical channel and an RLC         entity linked to the logical channel.

Processing D

The following processing is performed for each of the RLC bearer configurations (RLC-BearerConfig) included in the rlc-BearerToAddModList information element received:

(D-1) in a case that the configuration of the current terminal apparatus includes the RLC bearer of the received logical channel identifier:

-   -   (D-1-1) in a case that information (reestablishRLC) indicating         re-establishment of the RLC is received:         -   (D-1-1-1) reestablish the RLC entity;     -   (D-1-2) reconfigure the RLC entity in accordance with the         configuration (rlc-Config) of the received RLC;     -   (D-1-3) reconfigure the logical channel in accordance with the         MAC logical channel configuration received         (mac-LogicalChannelConfig);

(D-2) Otherwise:

-   -   (D-2-1) in a case that the configuration of the logical channel         identity and the RLC for the SRB are not included:         -   (D-2-1-1) establish an RLC entity in accordance with the             predefined (default) configuration;     -   (D-2-2) Otherwise:         -   (D-2-2-1) establish an RLC entity in accordance with the RLC             configuration received (rlc-Config);     -   (D-2-3) in a case that the logical channel identity and MAC         logical channel configuration for the SRB are not included:         -   (D-2-3-1) configure the MAC entity corresponding to the             logical channel in accordance with the predefined (default)             configuration;     -   (D-2-4) Otherwise:         -   (D-2-4-1) configure the MAC entity corresponding to the             logical channel in accordance with the MAC logical channel             configuration received;     -   (D-2-5) associate the logical channel with a PDCP entity, based         on identifier information (servedRadioBearer) of the radio         bearer included in the configuration of the RLC bearer.

Processing E

The following processing is performed:

(E-1) in a case that the reconfiguration target based on CellGroupConfig is the SCG and that SCG MAC is not part of the configuration of the current terminal apparatus:

-   -   (E-1-1) generate an SCG MAC entity;

(E-2) reconfigure the MAC main configuration of the cell group in accordance with MAC cell group configurations (mac-Cell) other than configurations related to addition, modification, and/or release of a timing advance group (TAG);

(E-3) in a case that the MAC cell group configuration received includes information (tag-ToReleaseList) related to the release of the TAG:

-   -   (E-3-1) in a case that the identifier of the TAG included in         tag-ToReleaseList is part of the configuration of the current         terminal apparatus, release, for the identifier of each TAG, the         TAG indicated by the identifier of the TAG;

(E-4) in a case that the MAC cell group configuration received includes information (tag-ToAddModList) related to addition and/or modification of the TAG:

-   -   (E-4-1) in a case that the identifier of the TAG included in         tag-ToAddModList is not part of the configuration of the current         terminal apparatus, then for the identifier of each TAG:         -   (E-4-1-1) add the TAG corresponding to the identifier of the             TAG in accordance with the timing advance timer received;     -   (E-4-2) in a case that the identifier of the TAG included in         tag-ToAddModList is part of the configuration of the current         terminal apparatus, then for the identifier of each TAG:         -   (E-4-2-1) reconfigure the TAG corresponding to the             identifier of the TAG in accordance with the timing advance             timer received.

Processing F

The following processing is performed:

(F-1) in a case that the release has been triggered by receiving an SCell release list (sCellToReleaseList):

-   -   (F-1-1) for the value of each of the SCell indexes (sCellIndex)         included in sCellToReleaseList:         -   (F-1-1-1) in a case that the configuration of the current             terminal apparatus includes an SCell having a value of             sCellIndex:             -   (F-1-1-1-1) release the SCell.

Processing G

The following processing is performed:

(G-1) in a case that the SpCell configuration includes information of a timer and a constant (rlf-TimersAndConstants) related to radio link failure (RLF):

-   -   (G-1-1) configure a timer and a constant for the RLF for the         cell group in accordance with rlf-TimersAndConstants:

(G-2) otherwise, in a case that rlf-TimersAndConstants is not configured for the cell group:

-   -   (G-2-1) configure a timer and a constant for the RLF for the         cell group by using the values of the timer and the constant         received in system information;

(G-3) in a case that the SpCell configuration includes a dedicated SpCell configuration (spCellConfigDedicated):

-   -   (G-3-1) configure an SpCell in accordance with         spCellConfigDedicated;     -   (G-3-2) consider a Bandwidth part (BWP) indicated by the         identifier (firstActiveUplinkBWP-Id) of the first active uplink         BWP to be an active uplink BWP in a case that this configuration         is provided;     -   (G-3-3) consider a Bandwidth part (BWP) indicated by the         identifier (firstActiveDownlinkBWP-Id) of the first active         downlink BWP (Bandwidth part) to be an active downlink BWP in a         case that this configuration is provided;     -   (G-3-4) in a case that the dedicated SpCell configuration         received reconfigures the reference signal used for radio link         monitoring:         -   (G-3-4-1) in a case that the timer T310 corresponding to the             SpCell is running, stop the timer T310;         -   (G-3-4-2) stop the counters N310 and N311.

Processing H

The following processing is performed:

(H-1) among the values of sCellIndex included in sCellToAddModList, for each of the values that are not part of the configuration of the current terminal apparatus:

-   -   (H-1-1) add the SCell corresponding to sCellIndex;     -   (H-1-2) for the lower layer, configure the SCell to be         considered to be in the deactivated state;     -   (H-1-3) for each of the measurement identifiers in a list         (measIdList) of measurement identifiers corresponding to         variables (VarMeasConfig) holding measurement configurations:         -   (H-1-3-1a) in a case that the SCell is not applicable to the             measurement corresponding to the measurement identifier: and         -   (H-1-3-1b) in a case that the SCell is included in a list of             triggered cells (cellsTriggeredList) defined by variables             (VarMeasReportList) holding a measurement report for the             measurement identifier:             -   (H-1-3-1-1) delete the SCell from the list of trigger                 cells (cellsTriggeredList) defined by the variables                 (VarMeasReportList) holding the measurement report for                 the measurement identifier;

(H-2) among the values of sCellIndex included in the sCellToAddModList, for each of the values that are part of the configuration of the current terminal apparatus:

-   -   (H-2-1) change the configuration of the SCell corresponding to         sCellIndex.

Processing I

The following processing is performed:

(I-1) in a case that RadioBearerConfig includes srb3-ToRelease:

-   -   (I-1-1) release the PDCP entity and the SRB identity for the         SRB3;

(I-2) in a case that RadioBearerConfig includes SRB-ToAddModList:

-   -   (I-2-1) add and/or reconfigure an SRB;

(I-3) in a case that RadioBearerConfig includes drb-ToReleaseList:

-   -   (I-3-1) release the DRB by the processing J described below;

(I-4) in a case that RadioBearerConfig includes DRB-ToAddModList:

(I-4-1) add and/or reconfigure a DRB by the processing K described below;

(I-5) release all the SDAP entities that are not associated with the DRB and notify the upper layer of release of user plane resources for a PDU session associated with the SDAP entity released.

In the processing I described above, for MBB-HO, two configurations of the source configuration and the target configuration may be managed in the processing for adding, reconfiguring, and/or releasing an SRB, and instead of performing the processing I-1 and the processing I-2 for the target configuration, the processing I-1 and the processing I-2 may be used for reconfiguration for the current SRB configuration. In other words, the SRB may manage one configuration. In this case, for a case of failure in handover and the like, the SRB configuration for the source before reconfiguration for reversion may be separately held.

As the processing I-5, for MBB-HO, all the SDAP entities that are not linked to the DRB of the source configuration or the DRB of the target configuration may be released, to notify the upper layer of release of user plane resources for the PDU sessions linked to the SDAP entities released. For example, MBB-HO may be performed based on the RRC reconfiguration message including Reconfiguration With Sync. Until a message for releasing the source configuration (e.g., an RRC message or a MAC CE) is received in the target cell, the SDAP entities associated with one or both of the source DRB and the target DRB may not be released. In a case that the source DRB is released in response to reception of the message for releasing the source configuration, all the SDAP entities that are not linked to the (target) DRB may be released. The upper layer may be notified of release of user plane resources for PDU sessions linked to the SDAP entities released.

The above “receiving a message for releasing a source configuration” may be interpreted as detecting a certain request. The certain request may be interpreted as certain information. Detecting a certain request may refer to inclusion of a particular information element (e.g., an information element indicating release of a source configuration) in the RRC message received, inclusion of particular information (e.g., information indicating release of a source configuration) in the MAC control element received, or reception of the first uplink grant in the SpCell. Detecting a certain request may refer to a success in the random access procedure. Detecting a certain request may refer to a success in the random access procedure in one or both of (A) a case that Reconfiguration With Sync is included in the SpCellConfig and (B) a case that the random access procedure is triggered by the RRC entity by submitting, to the lower layer, a message notifying completion of RRC reconfiguration (e.g., an RRC connection reconfiguration complete message for LTE or an RRC reconfiguration complete message for NR). Detecting a certain request may refer to something detected by implementation of the terminal apparatus.

Processing J

The following processing is performed:

(J-1a) for each of the DRB identities included in drb-ToReleaseList and that are part of the configuration of the current terminal apparatus: or

(J-1b) for each of the DRB identities released as a result of the full configuration:

-   -   (J-1-1) release the PDCP entity and the DRB identity;     -   (J-1-2) in a case that the SDAP entity linked to the DRB is         configured:         -   (J-1-2-1) indicate to the SDAP linked to the DRB the release             of the DRB;     -   (J-1-3) in a case that the DRB is linked to the identity of an         EPS bearer;         -   (J-1-3-1) in a case that no new bearer is added in the NR or             the E-UTRA by using an identical EPS bearer identity:         -   (J-1-3-1-1) notify the upper layer of release of the DRB and             the EPS bearer identity of the released DRB.

As the processing J-1-3-1, for MBB-HO, in a case that no new bearer is added in the source or target configuration for the identical EPS bearer, the upper layer may be notified of release of the DRB and the EPS bearer identity of the DRB released. For example, MBB-HO may be performed based on the RRC reconfiguration message including Reconfiguration With Sync. Until a message for releasing the source configuration (e.g., an RRC message, a MAC CE, or the like) is received in the target cell, the upper layer may not be notified of release of the DRB or the EPS bearer identity of the DRB released in a case that the bearer is linked in one of the source and target configurations for the identical EPS bearer. In a case that the source DRB is released in response to reception of the message for releasing the source configuration, the upper layer may be notified of release of the DRB or the EPS bearer identity of the DRB released in a case that no new bearer is added in the NR or the E-UTRA by using the identical EPS bearer identity.

Processing K

The following processing is performed:

(K-1) for each of the DRB identities included in DRB-ToAddModList and not being part of the configuration of the current terminal apparatus:

-   -   (K-1-1) establish a PDCP entity and configure the PDCP entity in         accordance with a PDCP configuration received (pdcp-Config);     -   (K-1-2) in a case that the PDCP entity of the DRB is not         configured due to disabled ciphering (cipheringDisabled):         -   (K-1-2-1a) in a case that the target RAT of handover is             E-UTRA/5GC: or         -   (K-1-2-1b) in a case that the terminal apparatus connects             only to the E-UTRA/5GC:             -   (K-1-2-1-1) configure the PDCP entity using a ciphering                 algorithm in NPL 4 and a key configuration;         -   (K-1-2-2) Otherwise:             -   (K-1-2-2-1) configure the PDCP entity by using the                 ciphering algorithm in accordance with a security                 configuration (securityConfig) and apply a key that is                 indicated by a parameter (keyToUse) linked to a master                 key (KeNB or KgNB) or a secondary key (S-KgNB).     -   (K-1-3) in a case that the PDCP entity of the DRB is configured         for integrity protection:         -   (K-1-3-1) configure the PDCP entity by using an integrity             protection algorithm in accordance with the security             configuration (securityConfig) and apply the key that is             indicated by the parameter (keyToUse) linked to the master             key (KeNB or KgNB) or the secondary key (S-KgNB);     -   (K-1-4) in a case that an SDAP configuration (sdap-Config) is         included:         -   (K-1-4-1) in a case that no SDAP is present in the PDU             session received:             -   (K-1-4-1-1) establish an SDAP entity;             -   (K-1-4-1-2) in a case that no SDAP is present for the                 PDU session received before reception of this                 reconfiguration:             -   (K-1-4-1-2-1) notify the upper layer of establishment of                 user plane resources for that PDU session;         -   (K-1-4-2) configure the SDAP entity in accordance with the             SDAP configuration received and link the DRB to the SDAP             entity;     -   (K-1-5) in a case that the DRB is linked to the EPS bearer         identity:         -   (K-1-5-1) in a case that the DRB is configured for the             identical EPS bearer identity by the NR or E-UTRA before             reception of the reconfiguration:             -   (K-1-5-1-1) link the DRB established to the                 corresponding EPS bearer identity;         -   (K-1-5-2) Otherwise:             -   (K-1-5-2-1) notify the upper layer of the establishment                 of the DRB and the EPS bearer identity of the DRB                 established;

(K-2) for each of the DRB identities included in DRB-ToAddModList and being part of the configuration of the current terminal apparatus:

-   -   (K-2-1) in a case that parameter reestablishPDCP is set:         -   (K-2-1-1a) in a case that the target RAT of handover is the             E-UTRA/5GC: or         -   (K-2-1-1b) in a case that the terminal apparatus connects             only to the E-UTRA/5GC:             -   (K-2-1-1-1) in a case that the PDCP entity of the DRB is                 not configured due to disabled ciphering                 (cipheringDisabled):                 -   (K-2-1-1-1-1) configure the PDCP entity by using the                     ciphering algorithm in NPL 4 and the key                     configuration;         -   (K-2-1-2) Otherwise:             -   (K-2-1-2-1) in a case that the PDCP entity of the DRB is                 not configured due to disabled ciphering                 (cipheringDisabled):                 -   (K-2-1-2-1-1) configure the PDCP entity by using the                     ciphering algorithm in accordance with the security                     configuration (securityConfig) and apply the key                     that is indicated by the parameter (keyToUse) linked                     to the master key (KeNB or KgNB) or the secondary                     key (S-KgNB);             -   (K-2-1-2-2) in a case that the PDCP entity of the DRB is                 configured for integrity protection:                 -   (K-2-1-2-2-1) configure the PDCP entity by using the                     integrity protection algorithm in accordance with                     the security configuration (securityConfig) and                     apply the key that is indicated by the parameter                     (keyToUse) linked to the master key (KeNB or KgNB)                     or the secondary key (S-KgNB);         -   (K-2-1-3) in a case that drb-ContinueROHC is included in             pdcp-Config:             -   (K-2-1-3-1) notify the lower layer that drb-ContinueROHC                 is configured;         -   (K-2-1-4) re-establish a PDCP entity of the DRB;     -   (K-2-2) Otherwise, in a case that recoverPDCP is set:         -   (K-2-2-1) trigger performance of data recovery for the PDCP             entity of the DRB;     -   (K-2-3) in a case that a PDCP configuration is included:         -   (K-2-3-1) reconfigure the PDCP entity in accordance with the             PDCP configuration received;     -   (K-2-4) in a case that an SDAP configuration is included:         -   (K-2-4-1) reconfigure the SDAP entity in accordance with the             SDAP configuration received;         -   (K-2-4-2) in a case that a QFI value is configured for each             of the QFIs added by mappedQoS-FlowsToAdd, release the QFI             values sequentially starting with the oldest DRB.

As the above-described processing K-1-4-1-2, for MBB-HO, in a case that no SDAP for the PDU session received is present in the source configuration or the target configuration before reception of the reconfiguration, the upper layer may be notified of establishment of user plane resources for the PDU session. Alternatively, as the above-described processing K-1-4-1-2, for MBB-HO, in a case that no SDAP for the PDU session received is present in the source configuration before reception of the reconfiguration, the upper layer may be notified of establishment of user plane resources for the PDU session.

In the above-described processing K-1-5-2, for MBB-HO, in a case that the DRB is not configured in the source or target configuration for the identical EPS bearer identity by the NR or the E-UTRA before reception of the reconfiguration, the upper layer may be notified of establishment of a DRB and the EPS bearer identity of the DRB established. Alternatively, in the above-described processing K-1-5-2, for MBB-HO, in a case that the DRB is not configured in the source configuration for the identical EPS bearer identity by the NR or the E-UTRA before reception of the reconfiguration, the upper layer may be notified of establishment of a DRB and the EPS bearer identity of the DRB established.

Processing L

The following processing is performed:

(L-1) in a case that the terminal apparatus is connected to the E-UTRA/EPC:

-   -   (L-1-1) in a case that sk-Counter is received:         -   (L-1-1-1) update the S-KgNB key based on the KgNB key and             the sk-Counter received;         -   (L-1-1-2) derive a KRRCenc key and a KUPenc key. The KRRCenc             key is a key used to protect the RRC signal generated from             KgNB in accordance with the ciphering algorithm. The KUPenc             is a key used to protect user plane traffic (user data)             generated from KgNB in accordance with the ciphering             algorithm;         -   (L-1-1-3) derive the KRRCint key and the KUPint key from the             KgNB key. The KRRCint key is a key used to protect the RRC             signal generated from KgNB in accordance with the integrity             algorithm. Additionally, the KUPint is a key used to protect             user plane traffic (user data) generated from KgNB in             accordance with the integrity algorithm.

(L-2) Otherwise:

-   -   (L-1-2) in a case that masterKeyUpdate received includes         nas-Container:         -   (L-1-2-1) forward the nas-Container to the upper layer;     -   (L-1-3) in a case that keySetChangeIndicator is true:         -   (L-1-3-1) derive or update KgNB based on KAMF;     -   (L-1-4) Otherwise:         -   (L-1-4-1) derive or update a KgNB key based on the current             KgNB key or NextHop (NH);     -   (L-1-5) store the value of nextHopChainingCount;     -   (L-1-6) derive a key associated with the KgNB key as follows;         -   (L-1-6-1) in a case that SecurityConfig includes             securityAlgorithmConfig:             -   (L-1-6-1-1) derive a KRRCenc key and a KUPenc key linked                 to cipheringAlgorithm included in                 securityAlgorithmConfig from the KgNB key;             -   (L-1-6-1-2) derive a KRRCint key and a KUPint key linked                 to integrityProtAlgorithm included in                 securityAlgorithmConfig from the KgNB key;         -   (L-1-6-2) Otherwise:             -   (L-1-6-2-1) derive a KRRCenc key and a KUPenc key linked                 to the current cipheringAlgorithm from the KgNB key:             -   (L-1-6-2-2) derive a KRRCint key and a KUPint key linked                 to the current integrityProtAlgorithm from the KgNB key.

An example of the operation of MBB-HO will be described. Here, an example will be described in which in the LTE, an RRC connection reconfiguration message is used that includes mobility control information (mobilityControlInfo) information elements. Note that the description of processing below includes description of reception of an information element but that this means that the information element is included in the RRC connection reconfiguration message triggering the processing unless otherwise indicated. The information element used in processing may be associated with the information element used in NPL 4 unless otherwise indicated.

The terminal apparatus receives the RRC connection reconfiguration message including mobilityControlInfo, and, in a case that the terminal apparatus can respond to the configuration included in the message, the terminal apparatus performs the following processing LA.

Processing LA

The following processing is performed:

(LA-1) start the timer T304 using a timer value of t304 included in mobilityControlInfo;

(LA-2) in a case that carrierFreq is included:

-   -   (LA-2-1) consider a cell operating on a frequency indicated by         carrierFreq and having a physical cell identity indicated by         targetPhysCellId to be the target PCell;

(LA-3) Otherwise:

-   -   (LA-3-1) consider a cell operating on the frequency of the PCell         of the source and having a physical cell identity indicated by         targetPhysCellId to be the target PCell;

(LA-4) initiate downlink synchronization in the target PCell;

(LA-5) in a case that makeBeforeBreak is configured:

-   -   (LA-5-1) after the terminal apparatus stops uplink transmission         to and/or downlink reception from the source cell, performs the         subsequent remaining processing of the procedure including         resetting of MAC;

(LA-6) in a case that makeBeforeBreak-r16 is configured:

(LA-6-1) replicate the configuration of the current terminal apparatus (source configuration) as a target configuration, and the subsequent reconfiguration processing may be performed on the replicated target configuration unless otherwise indicated. For example, the “configuration of the current terminal apparatus” for processing may be, for MBB-HO, considered to be the “target configuration of the current terminal apparatus.” For example, the configuration to be replicated may include some or all of (1) the configuration of the bearer (e.g., the SRB configuration, the DRB configuration, and the like), (2) the configuration of the cell group (e.g., the SpCell configuration, the SCell configuration, the RLC entity configuration, the MAC entity configuration, a PHY configuration, and the like), (3) internal variables (the measurement configuration (VarMeasConfig), measurement results (VarMeasReportList), the timer, the counter, etc.), and (4) the configuration related to security (e.g., the keys). The configuration of the bearer to be replicated may exclude the SRB configuration. Specifically, for the DRB, both the source configuration and the target configuration may be managed, and for the SRB, with the replication of the configuration being avoided, the source configuration may be switched to the target configuration. Information enabling determination of whether to replicate the SRB configuration may be included in the RRC connection reconfiguration message including mobilityControlInfo. For example, the above-described information may be included in MakeBeforeBreak-r16;

(LA-7) reset the MAC of the MCG and the MAC of the SCG in a case that these are configured. In a case that the MakeBeforeBreak-r16 is configured, the MAC of the source MCG and the MAC of the SCG need not be reset. Alternatively, in a case that MakeBeforeBreak-r16 is configured, the target MAC may be reset without resetting the source MAC;

(LA-8) re-establish a PDCP for all radio bearers that have been configured by the PDCP configuration and established. In a case that MakeBeforeBreak-r16 is configured, re-establishment of the PDCP is applied only to the target PDCP. Alternatively, for Single PDCP described below, in a case that MakeBeforeBreak-r16 is configured and that a PDCP is already present to which the target radio bearer is linked, the establishment and/or re-establishment of a PDCP need not be performed. In other words, in a case that MakeBeforeBreak-r16 is configured, this may allow a PDCP to be established and/or re-established in a case that no PDCP is present that is linked to the target radio bearer;

(LA-9) re-establish the RLC of the MCG and the RLC of the SCG for all radio bearers established in a case that this configuration is provided;

(LA-10) apply the value of newUE-Identity as a C-RNTI;

(LA-11) configure the lower layer in accordance with a cell common radio resource configuration received (radioResourceConfigCommon);

(LA-12) configure the lower layer in accordance with other information included in mobilityControlInfo received;

(LA-13) in a case that the RRC connection reconfiguration message received includes sCellToReleaseList:

-   -   (LA-13-1) release the SCell;

(LA-14) in a case that the RRC connection reconfiguration message received includes sCellGroupToReleaseList:

-   -   (LA-14-1) release the SCell group;

(LA-15a) in a case that the RRC connection reconfiguration message received includes scg-Configuration: or

(LA-15b) in a case that the configuration of the current terminal apparatus includes one or more split DRBs and that the RRC connection reconfiguration message received includes DRB-ToAddModList:

-   -   (LA-15-1) reconfigure the SCG;

(LA-16) in a case that the RRC connection reconfiguration message received includes a terminal apparatus-specific radio resource configuration (radioResourceConfigDedicated):

-   -   (LA-16-1) configure radio resources by processing LB described         below;

(LA-17) in a case that the RRC connection reconfiguration message includes a security configuration (securityConfigHO-v1530):

-   -   (LA-17-1) in a case that the nas-Container is received:         -   (LA-17-1-1) forward the nas-Container to the upper layer;     -   (LA-17-2) in a case that keyChangeIndicator-r15 is received and         that keyChangeIndicator-r15 is “true”:         -   (LA-17-2-1) update the KeNB key based on the KAMF key;     -   (LA-17-3) Otherwise:         -   (LA-17-3-1) update the KeNB key based on the current KeNB or             NextHop (NH);     -   (LA-17-4) store the value of nextHopChainingCount-r15;     -   (LA-17-5) in a case that securityAlgorithmConfig-r15 is         received:         -   (LA-17-5-1) derive a KRRCint key that is linked to             integrityProtAlgorithm received;         -   (LA-17-5-2) derive a KRRCenc key and a KUPenc key that are             linked to the cipheringAlgorithm received. The KRRCenc key             is a key used to protect the RRC signal generated from the             KeNB key in accordance with the ciphering algorithm. The             KUPenc is a key used to protect user plane traffic (user             data) generated from the KeNB key in accordance with the             ciphering algorithm;     -   (LA-17-6) Otherwise:         -   (LA-17-6-1) derive a KRRCint key linked to the current             integrityProtAlgorithm from the KeNB key;         -   (LA-17-6-2) derive a KRRCenc key and a KUPenc key linked to             the current cipheringAlgorithm from the KeNB key;

(LA-18) in a case that the RRC connection reconfiguration message received includes sCellToAddModList:

-   -   (LA-18-1) add and/or modify an SCell;

(LA-19) in a case that the received RRC connection reconfiguration message includes sCellGroupToAddModList:

-   -   (LA-19-1) add and/or modify an SCell group;

(LA-20) in a case that the RRC connection reconfiguration message received includes measConfig:

-   -   (LA-20-1) perform the measurement configuration;

(LA-21) perform automatic deletion of the measurement identifier;

(LA-22) submit the RRC connection reconfiguration complete message to the lower layer for transmission;

(LA-23) in a case that the MAC is successful in the random access procedure:

-   -   (LA-23-1) stop the timer T304 to terminate the procedure.

Processing LB

The following processing is performed:

(LB-1) in a case that radioResourceConfigDedicated received includes SRB-ToAddModList:

-   -   (LB-1-1) add and/or reconfigure an SRB by processing LC         described below;

(LB-2) in a case that radioResourceConfigDedicated received includes drb-ToReleaseList:

-   -   (LB-2-1) release the DRB by processing LD described below;

(LB-3) in a case that radioResourceConfigDedicated received includes DRB-ToAddModList:

-   -   (LB-3-1) add and/or reconfigure a DRB by processing LE described         below;

(LB-4) in a case that radioResourceConfigDedicated received includes mac-MainConfig:

-   -   (LB-4-1) perform the main configuration of the MAC by processing         LF described below.

Processing LC

The following processing is performed:

(LC-1) for each of the SRB identities included in the SRB-ToAddModList and being not part of the configuration of the current terminal apparatus:

-   -   (LC-1-1) establish a PDCP entity by using the current security         configuration;     -   (LC-1-2) in a case that rlc-BearerConfigSecondary with the value         “set up” is received:         -   (LC-1-2-1) establish a secondary MCG RLC entity in             accordance with rlc-BearerConfigSecondary received and             linked to a DCCH logical channel;         -   (LC-1-2-2) configure the PDCP entity of the E-UTRA to             activate duplication;

(LC-2) For each of the SRB identities included in SRB-ToAddModList and being part of the current terminal apparatus configuration:

-   -   (LC-2-1) in a case that pdcp-verChange is included (in other         words, NR PDCP is changed to E-UTRA PDCP):         -   (LC-2-1-1) establish an E-UTRA PDCP entity by using the             current security configuration;         -   (LC-2-1-2) link the primary RLC of the SRB to the PDCP             entity established;         -   (LC-2-1-3) release the NR PDCP of the SRB;     -   (LC-2-2) reconfigure a primary RLC entity in accordance with         rlc-Config received;     -   (LC-2-3) reconfigure a primary DCCH logical channel in         accordance with the logical channel configuration received         (logicalChannelConfig);     -   (LC-2-4) in a case that rlc-BearerConfigSecondary with the value         “release” is included:         -   (LC-2-4-1) release a secondary MCG RLC entity and a DCCH             logical channel linked to the secondary MCG RLC entity;     -   (LC-2-5) in a case that case that rlc-BearerConfigSecondary with         the value “set up” is received:         -   (LC-2-5-1) in a case that the secondary RLC bearer is not             included in the current SRB configuration:             -   (LC-2-5-1-1) establish a secondary MCG RLC entity in                 accordance with rlc-BearerConfigSecondary received and                 link the secondary MCG RLC entity to the DCCH logical                 channel;             -   (LC-2-5-1-2) configure the PDCP entity of the E-UTRA to                 activate duplication;         -   (LC-2-5-2) Otherwise:             -   (LC-2-5-2-1) reconfigure the secondary MCG RLC entity in                 accordance with rlc-BearerConfigSecondary received and                 link the secondary MCG RLC entity to the DCCH logical                 channel.

Processing LD

The following processing is performed:

(LD-1a) for each of the DRB identities included in drb-ToReleaseList and that are part of the configuration of the current terminal apparatus: or

(LD-2b) for each of the values of the DRB identities released as a result of the full configuration:

-   -   (LD-2-1) in a case that the release of the DRB results from full         configuration:         -   (LD-2-1-1) release the PDCP entity of the E-UTRA or NR;     -   (LD-2-2) Otherwise, in a case that the DRB is configured with a         PDCP: configuration,         -   (LD-2-2-1) release the PDCP entity of the E-UTRA;     -   (LD-2-3) Otherwise:         -   (LD-2-3-1) re-establish the RLC entity for the DRB;     -   (LD-2-4) release the RLC entity;     -   (LD-2-5) release a DTCH logical channel;     -   (LD-2-6) in a case that the terminal apparatus is connected to         the EPC:         -   (LD-2-6-1) in a case that the DRB is configured with the             PDCP configuration and no new DRB is added by             DRB-ToAddModList, nr-radioBearerConfig1, or             nr-radioBearerConfig2 by using an identical EPS bearer             identity:             -   (LD-2-6-1-1) in a case that the procedure has been                 triggered by handover:                 -   (LD-2-6-1-1-1) after the success of handover, notify                     the upper layer of release of the DRB and the EPS                     bearer identity of the DRB released;             -   (LD-2-6-1-2) Otherwise:                 -   (LD-2-6-1-2-1) notify the upper layer of the release                     of the DRB and the EPS bearer identity of the                     released DRB immediately.

Processing LE

The following processing is performed:

(LE-1) for each of the DRB identities included in DRB-ToAddModList and not being part of the configuration of the current terminal apparatus:

-   -   (LE-1-1) in a case that DRB-ToAddModListSCG has not been         received or DRB-ToAddModListSCG does not include the value of         the DRB identity:         -   (LE-1-1-1) in a case that pdcp-Config is included, establish             a PDCP entity in accordance with the pdcp-Config and             configured by using the current MCG security configuration:         -   (LE-1-1-2) in a case that rlc-Config is included, establish             an MCG RLC in accordance with rlc-Config:         -   (LE-1-1-3) in a case that a logical channel identity             (logicalChannelIdentity) and a logical channel configuration             (logicalChannelConfig) are included, establish an MCG DTCH             logical channel in accordance with logicalChannelIdentity             and logicalChannelConfig;         -   (LE-1-1-4) in a case that rlc-BearerConfigSecondary with the             value “setup,” is included:             -   (LE-1-1-4-1) establish a secondary MCG RLC entity and                 link the secondary MCG RLC entity to the DTCH logical                 channel in accordance with rlc-BearerConfigSecondary.                 The RLC entity established is then linked to an E-UTRA                 PDCP with an identical value of the DRB identity in the                 configuration of the current terminal apparatus;     -   (LE-1-2) in a case that the DRB is configured with an identical         EPS bearer identity:         -   (LE-1-2-1) link the DRB established to the EPS bearer             identity of the DRB;     -   (LE-1-3) Otherwise, in a case that the entries of         DRB-ToAddModList include pdcp-config (the bearer is established         by the PDCP of the E-UTRA):         -   (LE-1-3-1) notify the upper layer of establishment of the             DRB and the EPS bearer identity of the DRB established;

(LE-2) for each of the DRB identities included in DRB-ToAddModList and being part of the configuration of the current terminal apparatus:

-   -   (LE-2-1) reconfigure each layer and/or bearer in accordance with         the configuration included.

Processing LF

The following processing is performed:

(LF-1) reconfigure the MAC main configuration in accordance with MA main configuration information elements (mac-MainConfig) other than configurations related to addition, modification, and/or release of a secondary timing advance group (STAG);

(LF-2) in a case that mac-MainConfig received includes information related to the release of the STAG (stag-ToReleaseList):

-   -   (LF-2-1) in a case that the identity of the STAG included in         stag-ToReleaseList is part of the configuration of the current         terminal apparatus, release, then for each identifier of each         STAG, the STAG indicated by the STAG identifier;

(LF-3) in a case that mac-MainConfig received includes information related to the addition and/or modification of the stag (stag-ToAddModList):

-   -   (LF-3-1) in a case that the identifier of the STAG included in         stag-ToAddModList is not part of the configuration of the         current terminal apparatus, for the identifier of each TAG:         -   (LF-3-1-1) add the STAG corresponding to the identifier of             the STAG in accordance with timeAlignmentTimerSTAG received;     -   (LF-3-2) in a case that the identity of the STAG included in         stag-ToAddModList is part of the configuration of the current         terminal apparatus, then for the identifier of each STAG:         -   (LF-3-2-1) reconfigure the STAG corresponding to the             identifier of the STAG in accordance with             timeAlignmentTimerSTAG received.

Another example of the operation of the MBB-HO will be described. In this regard, an example will be described in which in the NR, an RRC reconfiguration message including a conditional handover configuration is used.

For example, the RRC message transmitted by the base station apparatus may include a conditional handover information element. The conditional handover information element may include a list including one or more information elements (conditional handover configurations) including information included in the Reconfiguration With Sync information element. The conditional handover information element may include, for each or some or all of the conditional handover configurations, an information element (conditional handover condition) indicating a condition for applying the conditional handover configuration.

The conditional handover configurations may include part or all of the information included in RadioBearerConfig and CellGroupConfig. The conditional handover configurations may include information indicating MBB-HO. The conditional handover condition may include threshold information for determining whether the condition is satisfied, by using a reference signal. The conditional handover condition may also include information indicating that the conditional handover configuration is to be applied immediately. For example, in a case that the conditional handover condition indicates information indicating that the conditional handover configuration is to be immediately applied and that the conditional handover configuration includes information indicating MBB-HO, MBB-HO can be implemented by performing the processing A and the processing I, based on the information included in the conditional handover configuration. Of course, even in a case that the conditional handover condition is another condition, and this condition is satisfied, conditional MBB-HO can be implemented by performing the processing A and the processing I, based on the information included in the conditional handover configuration.

In the MBB-HO of the NR, the terminal apparatus may take a PDCP (Single PDCP) configuration common to the source and the target.

For example, in a case that the core network is a 5GC, then in the source configuration, the logical channel, the DRB (or SRB), and the RLC bearer are linked together by the RLC bearer configuration, and the DRB, the PDCP entity, and the PDU session are linked together by drb-ToAddMod. Similarly, also in the target configuration, the logical channel, the DRB (or SRB), and the RLC bearer are linked together by the RLC bearer configuration, and the DRB (or SRB), the PDCP entity, and the PDU session are linked together by drb-ToAddMod. In this case, for example, the logical channel, the DRB (or SRB), and/or the RLC bearer linked to the identical DRB identity (or SRB identity) for the source and target configurations may be linked to one PDCP. For example, the logical channel, the DRB (or SRB), and/or the RLC bearer linked to the identical PDU session for the source and target configurations may be linked to one PDCP.

For example, in a case that the core network is a 5GC, then in the source configuration, the logical channel, the DRB (or SRB), and the RLC bearer are linked together by the RLC bearer configuration, and the DRB, the PDCP entity, and the PDU session are linked together by drb-ToAddMod. Similarly, also in the target configuration, the logical channel, the DRB (or SRB), and the RLC bearer are linked together by the RLC bearer configuration, and the DRB (or SRB), the PDCP entity, and the PDU session are linked together by drb-ToAddMod. In this case, for example, the logical channel, the DRB (or SRB), and/or the RLC bearer linked to the identical DRB identity (or SRB identity) for the source and target configurations may be linked to one SDAP.

For example, in a case that the core network is an EPC, in the source configuration, the DRB (or SRB), the PDCP entity, the logical channel, the RLC entity (and/or the RLC bearer), and the EPS bearer are linked together. Similarly, in the target configuration, the DRB (or SRB), the PDCP entity, the logical channel, the RLC entity (and/or the RLC bearer), and the EPS bearer are linked together. In this case, for example, the logical channel and the RLC entity (and/or RLC bearer) linked to the identical DRB identity (or SRB identity) for the source and target configurations may be linked to one PDCP entity. For example, the logical channel, the RLC entity (and/or RLC bearer), and the DRB (or SRB) linked to the identical EPS bearer identity for the source and target configurations may be linked to one PDCP.

In the above-described case, the terminal apparatus may consider the PDCP configurations of the source and the target linked to one PDCP to be identical. Alternatively, the terminal apparatus may apply the target PDCP configuration to the source PDCP configuration.

In a case that the source DRB (or SRB) and the target DRB including the identical DRB identity are linked to one PDCP entity, because the source and the target use different security keys (e.g., KUPenc, KUPint, KRRCenc, and/or KRRCint, and the like), multiple security keys are managed in one PDCP entity.

Another example of the operation of the MBB-HO will be described. In this regard, an example will be described in which in the LTE, the RRC connection reconfiguration message including the conditional handover configuration is used.

For example, the RRC message transmitted by the base station apparatus may include a conditional handover information element. The conditional handover information element may include a list including one or more information elements (conditional handover configurations) including information included in the mobilityControlInfo information element. The conditional handover information element may include, for each or some or all of the conditional handover configurations, an information element (conditional handover condition) indicating a condition for applying the conditional handover configuration.

The conditional handover configuration may include part or all of the information included in the cell common radio resource configuration (radioBearerConfigCommon) and the terminal apparatus-specific radio resource configuration (radioBearerConfigDedicated). The conditional handover configuration may include information indicating MBB-HO (e.g., MakeBeforeBreak-r16). The conditional handover condition may include threshold information for determining whether the condition is satisfied, by using a reference signal. The conditional handover condition may also include information indicating that the conditional handover configuration is to be applied immediately. For example, in a case that the conditional handover condition indicates information indicating that the conditional handover configuration is to be immediately applied, and the conditional handover configuration includes the information indicating MBB-HO, the processing LA is performed based on the information included in the conditional handover configuration, to implement MBB-HO. Of course, even in a case that the conditional handover condition is another condition, in a case that this is satisfied, the processing LA is performed based on information included in the conditional handover configuration, to implement conditional MBB-HO.

In the MBB-HO of the LTE above (MakeBeforeBreak-r16), for the terminal apparatus, the source and the target may take a common PDCP (Single PDCP) configuration.

For example, in a case that the core network is a 5GC, then in the source configuration, the logical channel, the DRB (or SRB), and the RLC bearer are linked together by the RLC bearer configuration, and the DRB, the PDCP entity, and the PDU session are linked together by drb-ToAddMod. Similarly, also in the target configuration, the logical channel, the DRB (or SRB), and the RLC bearer are linked together by the RLC bearer configuration, and the DRB (or SRB), the PDCP entity, and the PDU session are linked together by drb-ToAddMod. In this case, for example, the logical channel, the DRB (or SRB), and/or the RLC bearer linked to the identical DRB identity (or SRB identity) for the source and target configurations may be linked to one PDCP. For example, the logical channel, the DRB (or SRB), and/or the RLC bearer linked to the identical PDU session for the source and target configurations may be linked to one PDCP.

For example, in a case that the core network is a 5GC, then in the source configuration, the logical channel, the DRB (or SRB), and the RLC bearer are linked together by the RLC bearer configuration, and the DRB, the PDCP entity, and the PDU session are linked together by drb-ToAddMod. Similarly, also in the target configuration, the logical channel, the DRB (or SRB), and the RLC bearer are linked together by the RLC bearer configuration, and the DRB (or SRB), the PDCP entity, and the PDU session are linked together by drb-ToAddMod. In this case, for example, the logical channel, the DRB (or SRB), and/or the RLC bearer linked to the identical DRB identity (or SRB identity) for the source and target configurations may be linked to one SDAP.

For example, in a case that the core network is an EPC, in the source configuration, the DRB (or SRB), the PDCP entity, the logical channel, the RLC entity (and/or the RLC bearer), and the EPS bearer are linked together. Similarly, in the target configuration, the DRB (or SRB), the PDCP entity, the logical channel, the RLC entity (and/or the RLC bearer), and the EPS bearer are linked together. In this case, for example, the logical channel and the RLC entity (and/or RLC bearer) linked to the identical DRB identity (or SRB identity) for the source and target configurations may be linked to one PDCP entity. For example, the logical channel, the RLC entity (and/or RLC bearer), and the DRB (or SRB) linked to the identical EPS bearer identity for the source and target configurations may be linked to one PDCP.

In the above-described case, the terminal apparatus may consider the PDCP configurations of the source and the target linked to one PDCP to be identical. Alternatively, the terminal apparatus may apply the target PDCP configuration to the source PDCP configuration.

In a case that the source DRB and the target DRB (or SRB) including the identical DRB identity are linked to one PDCP entity, because the source and the target use different security keys (for example, KUPenc), the one PDCP entity manages the multiple security keys.

Note that information indicating whether to generate any of the layers of the target before connection to the target is completed may be included in the MakeBeforeBreak-r16.

Note that, in a case of NR, the following processing (E2-1) may be included in the (processing E) described above. For example, as illustrated in FIG. 22 , the processing (E2-1) may be performed between processing (E-1) and processing (E-2), but no such limitation is intended. In a case of LTE, the processing (E2-1) described below and the subsequent processing may be included in the (processing LF) described above. For example, the processing (E2-1) may be performed prior to the processing (LF-1), but no such limitation is intended.

(E2-1) in the case of an MBB-HO and in a case that a MAC entity for the target (also referred to as a secondary MAC entity) is not present as part of the configuration of the current terminal apparatus:

(E2-1-1) generate the secondary MAC entity.

Thus, the MAC entity can be generated appropriately in the processing based on the MAC layer configuration.

In a case of NR, the processing in the scope of the processing (B-9) of the (processing B) described above may be, for example, processing (B2-9) as illustrated in FIG. 23 . In the case of MBB-HO, the configuration for “this cell group” in the processing (B-9) and the subsequent processing in the processing (B) described above may be applied to the target.

(B2-9) in a case that Reconfiguration With Sync includes information indicating MBB-HO:

-   -   (B2-9-1) in a case that no MAC entity for the target (also         referred to as a secondary MAC entity) is present as part of the         current terminal apparatus:         -   (B2-9-1-1) not reset the MAC entity of this existing cell             group (also referred to as a primary MAC entity);         -   (B2-9-1-2) generate a secondary MAC entity;     -   (B2-9-2) apply an existing (default) MAC cell group         configuration to the secondary MAC entity. Alternatively, the         same configuration as that for the primary MAC entity may be         applied to the secondary MAC entity;     -   (B2-9-3) reset the secondary MAC entity;     -   (B2-9-4) consider the SCell of the target cell group to be in         the deactivated state in a case that this configuration has been         performed;     -   (B2-9-5) apply the value of newUE-Identity as the C-RNTI of this         cell group.

In LTE, processing in the scope from the processing (LA-6) to the processing (LA-7) in the (processing LA) described above may be processing (LA2-6) and processing (LA2-7) as illustrated in FIG. 24 , for example.

(LA2-6) in a case that makeBeforeBreak-r16 is configured:

-   -   (LA2-6-1) replicate the configuration of the current terminal         apparatus (source configuration) as a target configuration, and         the subsequent reconfiguration processing may be performed on         the replicated target configuration unless otherwise indicated.         For example, the “configuration of the current terminal         apparatus” for processing may be, for MBB-HO, considered to be         the “target configuration of the current terminal apparatus.”         For example, the configuration to be replicated may include some         or all of (1) the configuration of the bearer (e.g., the SRB         configuration, the DRB configuration, and the like), (2) the         configuration of the cell group (e.g., the SpCell configuration,         the SCell configuration, the RLC entity configuration, the MAC         entity configuration, a PHY configuration, and the like), (3)         internal variables (the measurement configuration         (VarMeasConfig), measurement results (VarMeasReportList), the         timer, the counter, etc.), and (4) the configuration related to         security (e.g., the keys). The configuration of the bearer to be         replicated may exclude the SRB configuration. Specifically, for         the DRB, both the source configuration and the target         configuration may be managed, and for the SRB, with the         replication of the configuration being avoided, the source         configuration may be switched to the target configuration.         Information enabling determination of whether to replicate the         SRB configuration may be included in the RRC connection         reconfiguration message including mobilityControlInfo. For         example, the above-described information may be included in         MakeBeforeBreak-r16. The above-described replication may involve         generation of each layer entity (e.g., RLC entity, MAC entity);     -   (LA2-6-2) in a case that no MAC entity for the target (also         referred to as the secondary MAC entity) is present as part of         the configuration of the current terminal apparatus:         -   (LA2-6-2-1) reset the MAC entity of this existing cell group             (also referred to as the primary MAC entity) is not reset;         -   (LA2-6-2-2) generate a secondary MAC entity;     -   (LA2-6-3) reset the secondary MAC entity if needed;

(L2A-7) Otherwise:

-   -   (LA2-7-1) reset the MAC of the MCG and the MAC of the SCG in a         case that this configuration is provided.

Accordingly, the MAC entity can be appropriately generated even in a case that the MAC cell group configuration is not included in the RRC reconfiguration message in NR. In a case that the MAC main configuration is not included in the RRC connection reconfiguration message in EUTRA, the MAC entity can be generated appropriately.

In the above-described (processing I), (processing J), or other processing, in response to receiving the message for releasing the source configuration, the terminal apparatus may release the current primary MAC entity and consider the current secondary MAC entity as the primary MAC entity. In response to receiving the message for releasing the source configuration, the terminal apparatus may reset the current primary MAC entity and consider the current secondary MAC entity as the primary MAC entity instead of considering the current primary MAC entity as the primary MAC entity.

Thus, the MAC entity can be appropriately managed.

Note that in each of the above-described processing operations, a handover (also referred to as an MBB-HO) may be performed in a case that makeBeforeBreak-r16 is included in the configuration of the master cell group, whereas a change of the secondary cell group (also referred to as an MBB-SCG Change) may be performed in a case that makeBeforeBreak-r16 is included in the configuration of the secondary cell group.

The terminal apparatus may notify the base station apparatus of some or all of the pieces of (1) information indicating whether to support performance of the MBB-HO or MBB-SCG Change in which communication using two or more cell groups (e.g. Dual Connectivity or Multi Connectivity) is maintained, (2) information indicating whether to support the performance of the MBB-HO in which communication using two or more cell groups (e.g. Dual Connectivity) is maintained, (3) information indicating whether to support the performance of the MBB-SCG Change in which communication using two or more cell groups (e.g. Dual Connectivity) is maintained, and (4) information indicating whether to support both the MBB-HO and MBB-SCG Change in which Dual Connectivity is maintained. For example, the information may be included in a message (for example, UECapabilityInformation) notifying the base station apparatus 3 of the radio access capability of the terminal apparatus. The information may be notified as information that is not dependent on the band combination supported by the terminal apparatus. The information may be notified as information for each band combination supported by the terminal apparatus. The information need not necessarily be notified to the base station apparatus.

The terminal apparatus may release one or more cell groups other than the MCG and perform the MBB-HO. The terminal apparatus may perform the above-described MBB-HO in a case that the terminal apparatus does not support the performance of the MBB-HO in which communication using two or more cell groups is maintained. The terminal apparatus may release one or more cell groups other than the MCG and perform the MBB-SCG Change. The terminal apparatus may perform the above-described MBB-SCG Change in a case that the terminal apparatus does not support the performance of the MBB-SCG Change in which communication using two or more cell groups is maintained. The terminal apparatus may perform a normal change of the secondary cell group (SCG Change) instead of the MBB-SCG Change. The terminal apparatus may perform the above-described change of the secondary cell group in a case that the terminal apparatus does not support the performance of the MBB-SCG Change in which communication using two or more cell groups is maintained. The SCG Change may be interpreted as SCG reconfiguration with sync. The handover (HO) may also be interpreted as MCG reconfiguration with sync.

Note that in a case that the configuration of the current terminal apparatus (configuration of the source) is replicated and is used as the configuration of the target ((A-0-1) and/or (LA-6-1) and/or (LA2-6-1) in the above), the value of a part or all of the timers retained inside the terminal apparatus may be handed over after the replication (in the target). In other words, the value before the replication (source) may be retained after the replication (target), and may be continued in the target, in other words, may be started or restarted from the value at the time of the replication. The value of a part or all of the timers need not be handed over after the replication (in the target). In other words, the value before the replication (source) may be initialized without being retained after the replication (target). In a case of being initialized, the value may be started or restarted from the value initialized in the target. Processing of handing over the value of a part or all of the timers in the source to the target may be performed in a part or all of the radio bearers. For example, in the SRB, the value of a part or all of the timers in the source may be handed over in the target, and in the DRB, the value of a part or all of the timers in the source may be initialized without being handed over to the target. The replicated timer may be the timers of a part or all of each entity of the PDCP entity, and/or the RLC entity, and/or the MAC entity. The replicated timer may include a part or all of the timers of the following (A) to (E):

(A) A discard timer being a timer started for an SDU every time when the SDU is received from the upper layer in the transmission side in the PDCP entity. In a case of expiry of the discard timer, the PDCP SDU may be discarded;

(B) A re-ordering timer being a timer used for detecting loss of a PDCP data PDU in the reception side of the PDCP entity. The timer may be a timer referred to as t-Reordering described in NPL 5 and/or NPL 11;

(C) A reassembly timer being a timer used for detecting loss of an RLC SDU in the reception side of the RLC entity. The timer may be a timer referred to as t-Reassembly described in NPL 6, and/or a timer referred to as t-Reordering in NPL 12;

(D) A poll retransmission timer being a timer used for retransmission of the poll in the transmission side of the RLC entity. The timer may be a timer referred to as t-PollRetransmit described in NPL 6 and/or NPL 12;

(E) A status prohibition timer being a timer used for prohibiting transmission of a status PDU in the reception side of the RLC entity. The timer may be a timer referred to as t-StatusProhibit described in NPL 6 and/or NPL 12.

Note that in a case that the configuration of the current terminal apparatus (configuration of the source) is replicated and is used as the configuration of the target ((A-0-1) and/or (LA-6-1) and/or (LA2-6-1) in the above), the value of a part or all of the variables such as a state variable and a counter retained inside the terminal apparatus may be handed over after the replication (in the target). In other words, the value before the replication (source) may be retained after the replication (target), and may be continued in the target, in other words, may be started or restarted from the value at the time of the replication. The value of a part or all of the variables such as a state variable and a counter may be handed over after the replication (in the target). In other words, the value before the replication (source) may be initialized without being retained after the replication (target). In a case of being initialized, the value may be started or restarted from the value initialized in the target. Processing of handing over the value of a part or all of the variables such as a state variable and a counter in the source to the target may be performed in a part or all of the radio bearers. For example, in the SRB, the value of a part or all of the variables such as a state variable and a counter in the source may be handed over in the target, and in the DRB, the value of a part or all of the variables such as a state variable and a counter in the source may be initialized without being handed over to the target. The replicated variables such as a state variable and a counter may be the variables such as a state variable and a counter of a part or all of each entity of the PDCP entity, and/or the RLC entity, and/or the MAC entity. In the replicated state variable and counter, a part or all of a state variable and a counter of the following (A) to (E) may be included:

(A) A state variable indicating a COUNT value of a PDCP PDU to be transmitted next in the transmission side of the PDCP entity. The state variable may be a state variable referred to as TX_NEXT described in NPL 11;

(B) A state variable indicating a COUNT value of a PDCP SDU expected to be received next in the reception side of the PDCP entity. The state variable may be a state variable referred to as RX_NEXT described in NPL 11;

(C) A state variable indicating a COUNT value of a first PDCP PDU among PDCP SDUs waiting to be received that are not distributed to the upper layer in the reception side of the PDCP entity. The state variable may be a state variable referred to as RX_DELIV described in NPL 11;

(C) A state variable indicating a COUNT value next to the COUNT value of the PDCP PDU that has started the re-ordering timer in the reception side of the PDCP entity. The state variable may be a state variable referred to as RX_REORD described in NPL 11.

FIG. 10 is an example of ASN.1 notation indicating the RRC connection reconfiguration message in the EUTRA in FIG. 4 . FIG. 11 is another example of the ASN.1 notation indicating the RRC connection reconfiguration message of the EUTRA in FIG. 4 . FIG. 12 is an example of the ASN.1 notation indicating the RRC reconfiguration message of the NR in FIG. 4 . FIG. 13 is another example of the ASN.1 notation indicating the RRC reconfiguration message of the NR in FIG. 4 .

In FIG. 10 and FIG. 11 , the information element represented by mobilityControlInfo is an information element including parameters related to mobility to the EUTRA for network control. Some or all of the pieces of information from (A) to (H) below may be included in the information element represented by mobilityControlInfo.

(A) Target physical cell identity

(B) t304 indicating information of the time from the start to the expiry of the timer T304

(C) newUE-Identity indicating a new identity (C-RNTI) of the UE 122

(D) Radio resource configuration

(E) Configuration of a dedicated random access channel

(F) makeBeforeBreak-r14 corresponding to a parameter for configuring existing (Release14) make before break-handover

(G) rach-Skip-r14 corresponding to a parameter for configuring RACH-less handover

(H) makeBeforeBreak-r16 corresponding to a parameter for configuring make before break-handover of the present embodiment

FIG. 10 illustrates an example where makeBeforeBreak-r16 is of an enumerated type, and FIG. 11 illustrates an example where makeBeforeBreak-r16 has, as a value, MakeBeforeBreak-r16 of the information element, and MakeBeforeBreak-r16 of the information element includes multiple fields.

In FIG. 12 and FIG. 13 , the information element represented by Reconfiguration With Sync is an information element including, for example, parameters related to handover of the PCell and the addition or change of the PSCell. The information element represented by Reconfiguration With Sync may include some or all of the pieces of information from (A) to (F) below.

(A) Configuration of the SpCell

(B) t304 indicating information of the time from the start to the expiry of the timer T304

(C) newUE-Identity indicating a new identity (RNTI) of the UE 122

(D) Configuration of a dedicated random access channel

(E) makeBeforeBreak-r16 corresponding to a parameter for configuring make before break-handover of the present embodiment

(F) rach-Skip-r16 corresponding to a parameter for configuring RACH-less handover

FIG. 12 illustrates an example where makeBeforeBreak-r16 is of an enumerated type, and FIG. 13 illustrates an example where makeBeforeBreak-r16 has, as a value, MakeBeforeBreak-r16 of the information element, and MakeBeforeBreak-r16 of the information element includes multiple fields.

Some or all of the fields illustrated in FIG. 10 to FIG. 13 may be optional. In other words, the fields illustrated in FIG. 10 to FIG. 13 may be included in the message depending on the condition.

Note that the eNB 102 or the gNB 108 may be allowed to provide a configuration as to whether to apply a make before break-handover (MBB-HO) for each radio bearer. In a case that a configuration as to whether to apply a make before break-handover is performed for each radio bearer, a parameter related to the make before break-handover may be configured below (in a layer below) the radio bearer configuration (information element indicated by SRB-ToAddMod and/or information element indicated by DRB-ToAddMod) or may be present below an information element indicated by PDCP-Config. In a case that a configuration as to whether to apply a make before break-handover is performed for each radio bearer, the information of the radio bearer to which the make before break-handover is applied may be allowed to be present above (in a layer above) the radio bearer configuration instead of allowing the parameter related to the make before break-handover to be present below the radio bearer configuration or the information element indicated by PDCP-Config.

FIG. 20 illustrates an example of ASN.1 indicating a parameter (information element or field) for a configuration as to whether to apply a make before break-handover (MBB-HO) to the radio bearer to be established or configured according to each embodiment of the present invention. In FIG. 20 , an example is illustrated in which a parameter is present below PDCP-Config, the parameter being used to provide a configuration as to whether to apply a make before break-handover to the radio bearer to be established or configured. However, the parameter may be present anywhere as long as the parameter is located below the radio bearer configuration. Note that “whether to apply a make before break-handover to the radio bearer to be established or configured” described above may be interpreted as a similar expression such as “whether the radio bearer to be established or configured performs a make before break-handover” or “whether it is the radio bearer to which make before break is applied”. Also, “whether to apply a make before break-handover to the radio bearer to be established or configured” described above may be interpreted as “whether to apply a make before break-handover to a PDCP entity,” or “whether the PDCP entity performs a make before break-handover,” or “the PDCP entity has a second configuration and a third configuration.” The second configuration described above may be a source (handover source) configuration in the handover. The third configuration described above may be a target (handover destination) configuration in the handover. The second configuration described above may be a primary configuration. The third configuration described above may be a secondary configuration. Any other expression may be used as long as the expression means that a make before break-handover is performed with both source configuration and target configuration configured and/or both primary configuration and secondary configuration configured for one PDCP entity.

In the example in FIG. 20 , a field expressed by mbb-drb is used as a parameter as to “whether to apply a make before break-handover to the radio bearer to be established or configured.” However, a field and/or information element with any other name may be used. FIG. 20(A) illustrates an example in which mbb-drb is of an enumerated type, and FIG. 20(B) illustrates an example in which mbb-drb has the information element MBB-DRB as a value and in which the information element MBB-DRB includes one or more fields. In FIG. 20(A), in a case that the information element includes a field expressed by mbb-drb or that the field is true, this may indicate that a make before break-handover is applied to the PDCP entity configured by this PDCP-Config and/or the radio bearer to which the PDCP entity is linked. In FIG. 20(B), the MBB-DRB information element includes, as a configuration for the handover destination, some or all of an identifier (field labeled targetCellGroupId) of a cell group corresponding to the handover destination, and a logical channel identifier (field labeled targetLogicalChannelIdentity) linked with this PDCP entity at the handover destination, and other parameters (not illustrated).

Note that the parameter may be as follows: the field expressed by mbb-drb as illustrated in FIG. 20 is optionally present only in a case that a parameter equivalent to makeBeforeBreak-r16 illustrated in the example in FIG. 10 to FIG. 13 is configured, whereas the field expressed by mbb-drb is not present in a case that no parameter equivalent to makeBeforeBreak-r16 illustrated in the example in FIG. 10 to FIG. 13 is configured.

FIG. 21 illustrates an example of ASN.1 in which the information of the radio bearer to which a make before break-handover is applied is present above the radio bearer configuration. As illustrated in FIG. 21 , as one of the parameters of information elements of MakeBeforeBreak-r16 in FIG. 11 and/or FIG. 13 (e.g., parameterA or parameterB illustrated in FIG. 11 and/or FIG. 13 ), the information of the radio bearer to which a make before break-handover is applied may be present. In the example in FIG. 21 , as parameters for the “information of the radio bearer to which a make before break-handover is applied,” the fields expressed by mbb-drb and mbb-drbList (list of mbb-drb) are used. However, fields and/or information elements with any other names may be used. As illustrated in FIG. 21 , the above-described information of the radio bearer to which a make before break-handover is applied may include some or all of a radio bearer identity (field expressed by drb-Identity) of the above-described radio bearer to which a make before break-handover is applied, and the identifier (field labeled targetCellGroupId) of the cell group corresponding to the handover destination, and the logical channel identifier (field labeled targetLogicalChannelIdentity) linked to this PDCP entity at the handover destination, and other parameters (not illustrated). In the example illustrated in FIG. 21 , in a case that no parameter for the “information of the radio bearer to which a make before break-handover is applied,” the make before break-handover may be applied to all of the radio bearers or all of the data radio bearers. Furthermore, although only the information of the data radio bearer (DRB) is illustrated as the “information of the radio bearer to which a make before break-handover is applied” in FIG. 21 , information of a signaling radio bearer (SRB) may be included.

FIG. 5 is a block diagram illustrating a configuration of the terminal apparatus (UE 122) according to each embodiment of the present invention. Note that FIG. 5 illustrates only the main components closely related to an aspect of the present invention in order to avoid complexity of description.

The UE 122 illustrated in FIG. 5 includes a receiver 500 configured to receive an RRC message and the like from a base station apparatus, a processing unit 502 configured to perform processing in accordance with any or all of pieces of configuration information such as various information elements (IEs), various fields, and various conditions included in the message received, and a transmitter 504 configured to transmit the RRC message and the like to the base station apparatus. The above-described base station apparatus may be the eNB 102 or the gNB 108. The processing unit 502 may include some or all of the functions of various layers (e.g., a physical layer, a MAC layer, an RLC layer, a PDCP layer, an RRC layer, and an NAS layer). In other words, the processing unit 502 may include some or all of a physical layer processing unit, a MAC layer processing unit, an RLC layer processing unit, a PDCP layer processing unit, an RRC layer processing unit, and an NAS layer processing unit.

FIG. 6 is a block diagram illustrating a configuration of the base station apparatus according to each embodiment of the present invention. Note that FIG. 6 illustrates only the main components closely related to one aspect of the present invention in order to avoid complexity of description. The above-described base station apparatus may be the eNB 102 or the gNB 108.

The base station apparatus illustrated in FIG. 6 includes a transmitter 600 configured to transmit an RRC message and the like to the UE 122, a processing unit 602 configured to create an RRC message including any or all of pieces of configuration information such as various information elements (IEs), various fields, and various conditions and to transmit the RRC message to the UE 122 to cause the processing unit 502 of the UE 122 to perform processing, and a receiver 604 configured to receive the RRC message and the like from the UE 122. The processing unit 602 may include some or all of the functions of various layers (e.g., the physical layer, the MAC layer, the RLC layer, the PDCP layer, the RRC layer, and the NAS layer). In other words, the processing unit 602 may include some or all of the physical layer processing unit, the MAC layer processing unit, the RLC layer processing unit, the PDCP layer processing unit, the RRC layer processing unit, and the NAS layer processing unit.

FIG. 25 is an example of a processing method of the UE 122 according to each embodiment of the present invention. The processing unit 602 of the base station apparatus (the eNB 102 and/or the gNB 108) creates a message related to reconfiguration of RRC connection for causing the UE 122 to perform processing, and transmits the message to the UE 122 from the transmitter 600 (not illustrated). The receiver 500 of the UE 122 receives the message related to reconfiguration of RRC connection transmitted from the base station apparatus (Step S2500).

The processing unit 502 of the UE 122 confirms whether or not first information is included in the message related to reconfiguration of RRC connection. In a case that the first information is not included, it may be determined that it is not the make before break-handover. In a case that the first information is included, it may be determined that it is the make before break-handover. In a case that the first information is included, it may be determined that the make before break-handover is applied or may be applied to a part or all of the radio bearers currently configured for the UE 122. In a case that the first information is included in the message related to reconfiguration of RRC connection, the processing unit 502 of the UE 122 may create a cell group and/or an MAC entity for the target of the make before break-handover. (Step S2502).

The processing unit 502 of the UE 122 may further confirm whether or not second information is included in the message related to reconfiguration of RRC connection, based on the fact that the first information is included. In a case that the second information is not included, it may be determined that the make before break-handover is not applied to all of the radio bearers currently configured for the UE 122. In a case that the second information is included, the radio bearer to which the make before break-handover is applied and/or the radio bearer to which the make before break-handover is not applied may be determined among the radio bearers currently configured for the UE 122, based on the second information (Step S2504).

Note that the first information in Step S2502 and/or Step S2504 may be information indicating the MBB-HO. The first information may be included in the mobilityControlInfo information element as illustrated in FIG. 10 or FIG. 11 , or may be included in the reconfigurationWithSync information element as illustrated in FIG. 12 or FIG. 13 .

The processing unit 502 of the UE 122 may change or reconfigure a cell group associated with the RLC bearer of the radio bearer to which the make before break-handover is not applied from a first cell group to a second cell group (Step S2506).

The processing unit 502 of the UE 122 may establish a second RLC bearer for the radio bearer to which the make before break-handover is applied, and may associate the second RLC bearer with the PDCP entity of the radio bearer to which the make before break-handover is applied. In this case, the second RLC bearer may be associated with the second cell group (of Step S2506) (Step S2508).

Note that the second information in Step S2504, and/or Step S2506, and/or Step S2508 may be the information indicating whether or not the make before break-handover is applied to the established or configured radio bearer (illustrated in FIG. 21 and/or FIG. 22 ).

In Step S2506 and/or Step S2508, the second cell group may be a cell group that is generated based on the fact that the first information is included in the message related to reconfiguration of RRC connection in Step S2502.

In Step S2506, to change or reconfigure the cell group associated with the RLC bearer of the radio bearer to which the make before break-handover is not applied from the first cell group to the second cell group may be to perform operation including a part or all of operations of the following (A) and (B) for the RLC entity of the radio bearer to which the make before break-handover is not applied and/or the logical channel of the radio bearer to which the make before break-handover is not applied:

(A) Reconfigure the RLC entity of the first cell group as the RLC entity of the second cell group;

(B) Reconfigure the logical channel of the first cell group as the logical channel of the second cell group.

Note that the logical channel may be the DTCH logical channel. The first cell group may be the cell group associated with the radio bearer to which the make before break-handover is not applied before performing the make before break-handover.

In Step S2508, to associate the second RLC bearer with the second cell group may be to perform operation including a part or all of operations of the following (C) and (D):

(C) Configure or reconfigure the RLC entity of the second RLC bearer as the RLC entity of the second cell group;

(D) Configure or reconfigure the logical channel of the second RLC bearer as the logical channel of the second cell group.

Note that the logical channel may be the DTCH logical channel.

In Step S2506 and/or Step S2508, both of the first cell group and the second cell group may be a master cell group (MCG). In Step S2506 and/or Step S2508, the first cell group and the second cell group may be referred to as a first MAC entity and a second MAC entity, respectively. The second MAC entity may be a MAC entity for the target of the make before break-handover, which is generated in Step S2502 described above. The first cell group may be an MCG of the source in a case of the make before break-handover, and/or an MCG in a case that the make before break-handover is not performed. The second cell group may be an MCG of the target in a case of the make before break-handover. The first MAC entity may be a MAC entity of the source in a case of the make before break-handover, and/or a MAC entity in a case that the make before break-handover is not performed. The second MAC entity may be a MAC entity of the target in a case of the make before break-handover.

In Step S2506, the radio bearer to which the make before break-handover is not applied may be replicated before the cell group associated with the RLC bearer of the radio bearer to which the make before break-handover is not applied is changed from the first cell group to the second cell group. The replication of the radio bearer may be preparation of the radio bearer having the same configuration as the configuration of the radio bearer. The replication of the radio bearer may be preparation of the radio bearer having the same configuration as the configuration of the radio bearer and having the same data as the data being processed by the radio bearer. The data being processed by the radio bearer may include the PDU and/or the SDU retained by each layer, a buffer of each layer, the variable retained by each layer, the value of the timer, and the like. One of the radio bearer to which the make before break-handover is not applied and the replicated radio bearer may be stopped. The processing of “changing the cell group associated with the RLC bearer of the radio bearer to which the make before break-handover is not applied from the first cell group to the second cell group” in Step S2506 may be performed for the bearer that is not stopped. The stop of the radio bearer may include stop of uplink transmission, and may include stop of downlink reception.

Instead of performing the processing of Step S2504 described above, in Step S2502 described above, it may be determined that the make before break-handover is applied to all of the radio bearers, based on the fact that the first information is included in the message related to reconfiguration of RRC connection. In this case, the processing of Step S2506 described above need not be performed.

FIG. 26 is another example of a processing method of the UE 122 according to each embodiment of the present invention. The processing unit 502 of the UE 122 that attempts handover from the handover source to the handover target detects expiry of the first timer (Step S2600). Note that the first timer may be a timer used for detecting a handover failure or the like. The first timer may be a timer that starts in a case of receiving the message related to reconfiguration of RRC connection including a parameter for indicating handover (the information element referred to as MobilityControlInfo described in NPL 4, or the information element referred to as ReconfigurationWithSync described in NPL 10), or in a case of cell movement from a different RAT (CellChangeOrder described in NPL 4), and that stops in a case that the handover succeeds, or in a case that CellChangeOrder succeeds, or in a case that random access to a corresponding SpCell (of the handover target) succeeds. In a case that the first timer expires, it may be considered that the handover has failed. In a case that the first timer expires, the UE 122 may start the re-establishment procedure of RRC connection. In a case that the UE 122 starts re-establishment of RRC connection in a case that the first timer expires, the configuration of the UE 122 may be changed back to the configuration of the handover source. In a case that the first timer expires in a case of a handover to a different RAT, the re-establishment of RRC connection may be performed by selecting a cell of the handover source. The first timer may be the timer T304 described in NPL 4 or NPL 10. Note that, as described in NPL 3, the handover may be processing in which the UE 122 in the RRC connected state changes the serving cell. The handover may be processing performed in a case of receiving the message related to reconfiguration of RRC connection including a parameter for indicating handover (the information element referred to as MobilityControlInfo described in NPL 4, or the information element referred to as ReconfigurationWithSync described in NPL 10), or may be a message indicating movement to a cell of another RAT (for example, MobilityFromEUTRACommand described in NPL 4, or MobilityFromNRCommand described in NPL 10). The handover may be a DAPS handover.

In Step S2600, the processing unit 502 of the UE 122 that has detected expiry of the first timer may determine whether or not first configuration is performed for the UE 122 next. In a case that the first configuration is performed for the UE 122, a part or all of the configurations of the handover target may be released, based on the fact the first configuration is performed (Step S2602). Note that the first configuration may be a configuration related to the DAPS handover, or may be a configuration related to the radio bearer to which the DAPS handover is applied. The case that the first configuration is performed may be interpreted as a case that the configuration of the DAPS handover is performed for any one of the radio bearers, may be interpreted as a case that the configuration of the DAPS handover is performed for at least one of the radio bearers, or may be interpreted as another similar expression. The release of a part or all of the configurations of the handover target may be release of a configuration including a part or all of the RLC entity and the logical channel of the handover target for the radio bearer to which the DAPS handover is applied. The release of the configuration of the handover target may be release of a configuration including a part or all of the QoS flow and a corresponding rule of the radio bearer in the PDCP entity, the radio bearer identity, the RLC entity, the logical channel, and the SDAP of the handover target for the radio bearer to which the DAPS handover is not applied. In a case that the configuration of the handover target is released again, the MAC entity of the handover target may be reset.

In Step S2602, the processing unit 502 of the UE 122 may determine whether or not the first configuration is performed for the UE 122. In a case that the first configuration is performed for the UE 122, the processing unit 502 of the UE 122 may further determine whether or not a radio link failure is detected in the primary cell of the handover source. In a case that a radio link failure is not detected in the primary cell of the handover source, a part or all of the configurations of the handover target may be released, based on the fact that the first configuration is performed for the UE 122 and the fact that a radio link failure is not detected in the primary cell of the handover source. Note that the primary cell may be a Primary Cell (PCell), or may be a Special Cell (SpCell).

In Step S2600, the processing unit 502 of the UE 122 that detects expiry of the first timer may determine whether or not the first configuration is performed for the UE 122. In a case that the first configuration is performed for the UE 122, the processing unit 502 may perform update of a security key configured for the handover source, based on the fact that the first configuration is performed (Step S2604). Note that the first configuration may be a configuration related to the DAPS handover, or may be a configuration related to the radio bearer to which the DAPS handover is applied. The case that the first configuration is performed may be interpreted as a case that the configuration of the DAPS handover is performed for any one of the radio bearers, may be interpreted as a case that the configuration of the DAPS handover is performed for at least one of the radio bearers, or may be interpreted as another similar expression. The security key configured for the handover source may be interpreted as a security key having been configured for the handover source. The update of the security key may be processing including a part or all of the following (A) to (B):

(A) Derive a base station key from the current base station key or Next Hop (NH) information;

(B) Derive a part or all of a secrecy key for the SRB, an integrity key for the SRB, a secrecy key for the DRB, and an integrity key for the DRB.

In Step S2604, after update of the security key is performed, before update of the security key is performed, or without performing update of the security key, processing including a part or all of the following (C) to (F) may be performed.

(C) For a part or all of the SRBs, configure a lower layer so as to perform processing of integrity protection by using the integrity key for the SRB or the configured integrity key for the SRB, and configured integrity algorithm.

(D) For a part or all of the DRBs, configure a lower layer so as to perform processing of integrity protection by using by using the integrity key for the DRB or the configured integrity key for the DRB, and configured integrity algorithm.

(E) For a part or all of the SRBs, configure a lower layer so as to perform processing of ciphering by using the secrecy key for the SRB or the configured secrecy key for the SRB and configured secrecy algorithm.

(F) For a part or all of the DRBs, configure a lower layer so as to perform processing of ciphering by using the secrecy key for the DRB or the configured secrecy key for the DRB and configured secrecy algorithm.

Note that, in Step S2604, the base station key may be KeNB described in NPL 21, or may be KgNB described in NPL 21. In Step S2604, the integrity key for the SRB and the integrity key for the DRB may be KRRCint and KUPint described in NPL 21 and/or NPL 22, respectively. In Step S2604, the secrecy key for the SRB and the secrecy key for the DRB may be KRRCenc and KUPenc described in NPL 21 and/or NPL 22. In Step S2604, the Next Hop (NH) may be the Next Hop (NH) described in NPL 21 and/or NPL 22. In Step S2604, the lower layer may be a PDCP layer or a PDCP entity.

The processing of (C) described above in Step S2604 may be interpreted as configuration of a lower layer for all of the SRBs except the SRB 1 so as to perform processing of integrity protection by using the integrity key for the SRB or the configured integrity key for the SRB, and configured integrity algorithm. The processing of (E) described above in Step S2604 may be interpreted as configuration of a lower layer for all of the SRBs except the SRB 1 so as to perform processing of ciphering by using the secrecy key for the SRB or the configured secrecy key for the SRB and configured secrecy algorithm. A part or all of the processing in Step S2604 may be performed after the UE 122 detects expiry of the first timer and before transmitting a first RRC message to the base station apparatus of the handover source in Step S2600. A part or all of the processing in Step S2604 may be performed after the UE 122 detects expiry of the first timer and after transmitting a first RRC message to the base station apparatus of the handover source in Step S2600. The first RRC message may be an RRC message for notifying the target that the DAPS handover has failed. A lower layer may be configured for the SRB 1 or a part or all of the radio bearers so as to perform processing of integrity protection by using the integrity key for the SRB or the configured integrity key for the SRB, and configured integrity algorithm after transmitting the first RRC message to the base station apparatus of the handover source. A lower layer may be configured for the SRB 1 or a part or all of the radio bearers so as to perform processing of ciphering by using the secrecy key for the SRB or the configured secrecy key for the SRB and configured secrecy algorithm after transmitting the first RRC message to the base station apparatus of the handover source. In Step S2604, before performing update of the security key or after performing update of the security key, a part or all of the radio bearers may be suspended. After the UE 122 detects expiry of the first timer, a part or all of the suspended radio bearers may be resumed in a case of transmitting or before transmitting the first RRC message to the base station apparatus of the handover source. The resumed radio bearer may include the SRB 1, or may include all of the SRBs.

A part or all of the processing in Step S2604 may be performed in a case of receiving or after receiving the first RRC message from the base station apparatus of the handover source after the UE 122 detects expiry of the first timer in Step S2600. A part or all of the processing in Step S2604 may be performed based on the fact that the RRC message first received from the base station apparatus of the handover source includes a parameter meaning update of the security key after the UE 122 detects expiry of the first timer in Step S2600. The first RRC message received from the base station apparatus of the handover source may be a message related to reconfiguration of RRC connection, may be a message related to resumption of RRC connection, or may be another RRC message. The parameter meaning update of the security key may be included in the RRC message, based on the fact that the DAPS handover has failed. The parameter meaning update of the security key may be a parameter (field) referred to as securityConfigHO described in NPL 4, or may be a parameter (field) referred to as masterKeyUpdate described in NPL 10.

In Step S2604, the MAC entity of the handover source may be reset. The processing of resetting the MAC entity of the handover source may be performed before or after the update processing of the security key of the handover source, may be performed before transmitting the first RRC message to the base station apparatus of the handover source after the UE 122 detects expiry of the first timer, or may be performed after the first RRC message is transmitted. The processing of resetting the MAC entity of the handover source may be performed in a case of receiving or after receiving the first RRC message from the base station apparatus of the handover source after the UE 122 detects expiry of the first timer. In Step S2604, the PDCP entity of a part or all of the radio bearers may be reestablished before or after the update processing of the security key of the handover source.

In Step S2604, the processing unit 502 of the UE 122 may determine whether or not the first configuration is performed for the UE 122. In a case that the first configuration is performed for the UE 122, the processing unit 502 of the UE 122 may further determine whether or not a radio link failure is detected in the primary cell of the handover source. In a case that a radio link failure is not detected in the primary cell of the handover source, update of the security key configured for the handover source and the above processing may be performed, based on the fact that the first configuration is performed for the UE 122 and the fact that a radio link failure is not detected in the primary cell of the handover source. Note that the primary cell may be a Primary Cell (PCell), or may be a Special Cell (SpCell).

In Step S2604, processing of changing back (reverting) to the configuration used in the handover source may be performed for a part or all of the radio bearers, based on the fact that the first configuration is performed for the UE 122 and/or the fact that a radio link failure is not detected in the primary cell of the handover source. The processing of changing back (reverting) to the configuration used in the handover source may be performed for the radio bearer to which the DAPS handover is not applied. The processing of changing back (reverting) to the configuration used in the handover source for a part or all of the radio bearers may be performed before the update processing of the security key, may be performed after the update processing of the security key, may be performed before transmitting the first RRC message to the base station apparatus of the handover source after the UE 122 detects expiry of the first timer, or may be performed after transmitting the first RRC message in Step S2604.

Note that, in Step S2604, the update of the security key need not be performed based on the fact that the first configuration is performed for the UE 122 and/or the fact that a radio link failure is not detected in the primary cell of the handover source.

Note that, in Step S2604, the update of the security key need not be performed.

The receiver 500 of the UE 122 may receive a message related to reconfiguration of RRC connection from the base station apparatus. The processing unit 502 of the UE 122 may establish or reconfigure the radio bearer in accordance with the message related to reconfiguration of RRC connection (Step S2606). Note that a part or all of the processing of Step S2604 described above may be performed in a case of establishing or reconfiguring the radio bearer in Step S2606.

In Step S2604 and/or Step S2606, a part or all of the data present in a buffer may be discarded for a part or all of the radio bearers, based on the fact that the first configuration is performed for the UE 122 and/or the fact that a radio link failure is not detected in the primary cell of the handover source. The data present in the buffer may be a part or all of the PDCP SDU, the PDCP PDU, the RLC SDU, the RLC SDU segment, the RLC PDU, the MAC SDU, and the MAC PDU. The data present in the buffer may include data present in a retransmission buffer. The processing of discarding a part or all of data present in the buffer based on the fact that the first configuration is performed for the UE 122 and/or the fact that a radio link failure is not detected in the primary cell of the handover source may be performed after performing the processing of changing back (reverting) to the configuration used in the handover source for the radio bearer to which the DAPS handover is not applied. The processing of discarding a part or all of data present in the buffer based on the fact that the first configuration is performed for the UE 122 and/or the fact that a radio link failure is not detected in the primary cell of the handover source may be performed after performing the processing of changing back (reverting) to the configuration used in the handover source for the bearer (UM DRB) for which the RLC UM is configured or established among the radio bearers to which the DAPS handover is not applied. The processing of discarding a part or all of data present in the buffer based on the fact that the first configuration is performed for the UE 122 and/or the fact that a radio link failure is not detected in the primary cell of the handover source may be performed by a discard timer configured for the PDCP entity. The discard timer may be a timer referred to as discardTimer described in NPL 5 and/or NPL 11. The discard timer may be a timer that is started for an SDU every time when the SDU is received from the upper layer in the transmission side of the PDCP entity. In a case that the discard timer expires, the SDU may be discarded. As a value of the discard timer, a value of the discard timer in the target at the time point of expiry of the first timer may be applied. In other words, in a case of performing the processing of changing back (reverting) the radio bearer to the configuration used in the handover source, regarding the discard timer, the value of the discard timer in the target is retained without changing back to the configuration used in the source, and in the radio bearer changed back to the configuration used in the handover source, the value of the discard timer in the target may be continued. The radio bearer that performs the processing of discarding a part or all of data present in the buffer based on the fact that the first configuration is performed for the UE 122 and/or the fact that a radio link failure is not detected in the primary cell of the handover source may be configured in advance by an RRC message.

In Step S2604 and/or Step S2606, a part or all of the timers configured for each entity may be stopped, and/or started and/or restarted for a part or all of the radio bearers, based on the fact that the first configuration is performed for the UE 122 and/or the fact that a radio link failure is not detected in the primary cell of the handover source. The timer configured for each entity may be the timers of a part or all of each entity of the PDCP entity, and/or the RLC entity, and/or the MAC entity. The processing of stopping, and/or starting and/or restarting a part or all of the timers configured for each entity based on the fact that the first configuration is performed for the UE 122 and/or the fact that a radio link failure is not detected in the primary cell of the handover source may be performed after performing the processing of changing back (reverting) to the configuration used in the handover source for the radio bearer to which the DAPS handover is not applied. The processing of stopping, and/or starting and/or restarting a part or all of the timers configured for each entity based on the fact that the first configuration is performed for the UE 122 and/or the fact that a radio link failure is not detected in the primary cell of the handover source may be performed after performing the processing of changing back (reverting) to the configuration used in the handover source for the bearer (UM DRB) for which the RLC UM is configured or established among the radio bearers to which the DAPS handover is not applied. The radio bearer that performs the processing of stopping, and/or starting and/or restarting a part or all of the timers configured for each entity based on the fact that the first configuration is performed for the UE 122 and/or the fact that a radio link failure is not detected in the primary cell of the handover source may be configured in advance by an RRC message. The timer configured for each entity may include a part or all of the timers of the following (A) to (D):

(A) A re-ordering timer being a timer used for detecting loss of a PDCP data PDU in the reception side of the PDCP entity. The timer may be a timer referred to as t-Reordering described in NPL 5 and/or NPL 11;

(B) A reassembly timer being a timer used for detecting loss of an RLC SDU in the reception side of the RLC entity. The timer may be a timer referred to as t-Reassembly described in NPL 6, and/or a timer referred to as t-Reordering in NPL 12;

(C) A poll retransmission timer being a timer used for retransmission of the poll in the transmission side of the RLC entity. The timer may be a timer referred to as t-PollRetransmit described in NPL 6 and/or NPL 12;

(D) A status prohibition timer being a timer used for prohibiting transmission of a status PDU in the reception side of the RLC entity. The timer may be a timer referred to as t-StatusProhibit described in NPL 6 and/or NPL 12.

In Step S2604 and/or Step S2606, a part or all of the state variables configured for each e entity may be configured and/or reconfigured to the initial value for a part or all of the radio bearers, based on the fact that the first configuration is performed for the UE 122 and/or the fact that a radio link failure is not detected in the primary cell of the handover source. The state variables configured for each entity may be the state variables of a part or all of each entity of the PDCP entity, and/or the RLC entity, and/or the MAC entity. The processing of configuring and/or reconfiguring a part or all of the state variables configured for each entity to the initial value based on the fact that the first configuration is performed for the UE 122 and/or the fact that a radio link failure is not detected in the primary cell of the handover source may be performed after performing the processing of changing back (reverting) to the configuration used in the handover source for the radio bearer to which the DAPS handover is not applied. The processing of configuring and/or reconfiguring a part or all of the state variables configured for each entity to the initial value based on the fact that the first configuration is performed for the UE 122 and/or the fact that a radio link failure is not detected in the primary cell of the handover source may be performed after performing the processing of changing back (reverting) to the configuration used in the handover source for the bearer (UM DRB) for which the RLC UM is configured or established among the radio bearers to which the DAPS handover is not applied. The radio bearer that performs the processing of configuring and/or reconfiguring a part or all of the state variables configured for each entity to the initial value based on the fact that the first configuration is performed for the UE 122 and/or the fact that a radio link failure is not detected in the primary cell of the handover source may be configured in advance by an RRC message.

In Step S2604 and/or Step S2606, the configuration is changed back (reverted) to the configuration used in the handover source for a part or all of the radio bearers based on the fact that the first configuration is performed for the UE 122 and/or the fact that a radio link failure is not detected in the primary cell of the handover source, and in this case, processing of not changing back (reverting) a part or all of data to the configuration or the state used in the handover source may be performed. The part or all of data may be a part or all of the PDCP SDU, the PDCP PDU, the RLC SDU, the RLC SDU segment, the RLC PDU, the MAC SDU, and the MAC PDU. The configuration is changed back (reverted) to the configuration used in the handover source for a part or all of the radio bearers based on the fact that the first configuration is performed for the UE 122 and/or the fact that a radio link failure is not detected in the primary cell of the handover source, and in this case, the processing of not changing back (reverting) a part or all of data to the configuration or the state used in the handover source may be performed for the radio bearer to which the DAPS handover is not applied, or may be performed for the UM bearer to which the DAPS handover is not applied. The configuration is changed back (reverted) to the configuration used in the handover source for a part or all of the radio bearers based on the fact that the first configuration is performed for the UE 122 and/or the fact that a radio link failure is not detected in the primary cell of the handover source, and in this case, the radio bearer that performs the processing of not changing back (reverting) a part or all of data to the configuration or the state used in the handover source may be configured in advance by an RRC message.

In Step S2604 and/or Step S2606, the configuration is changed back (reverted) to the configuration used in the handover source for a part or all of the radio bearers based on the fact that the first configuration is performed for the UE 122 and/or the fact that a radio link failure is not detected in the primary cell of the handover source, and in this case, processing of starting or restarting the value of a part or all of the timers by configuring the initial value without changing back (reverting) to the configuration or the state used in the handover source may be performed. The configuration is changed back (reverted) to the configuration used in the handover source for a part or all of the radio bearers based on the fact that the first configuration is performed for the UE 122 and/or the fact that a radio link failure is not detected in the primary cell of the handover source, and in this case, the processing of starting or restarting the value of a part or all of the timers by configuring the initial value without changing back (reverting) to the configuration or the state used in the handover source may be performed for the radio bearer to which the DAPS handover is not applied, or may be performed for the UM bearer to which the DAPS handover is not applied. The configuration is changed back (reverted) to the configuration used in the handover source for a part or all of the radio bearers based on the fact that the first configuration is performed for the UE 122 and/or the fact that a radio link failure is not detected in the primary cell of the handover source, and in this case, the radio bearer that performs the processing of starting or restarting the value of a part or all of the timers by configuring the initial value without changing back (reverting) to the configuration or the state used in the handover source may be configured in advance by an RRC message. The part or all of the timers may include a part or all of the timers of the following (A) to (E):

(A) A discard timer being a timer started for an SDU every time when the SDU is received from the upper layer in the transmission side in the PDCP entity. In a case of expiry of the discard timer, the PDCP SDU may be discarded;

(B) A re-ordering timer being a timer used for detecting loss of a PDCP data PDU in the reception side of the PDCP entity;

(C) A reassembly timer being a timer used for detecting loss of an RLC SDU in the reception side of the RLC entity;

(D) A poll retransmission timer being a timer used for retransmission of the poll in the transmission side of the RLC entity;

(E) A status prohibition timer being a timer used for prohibiting transmission of a status PDU in the reception side of the RLC entity.

In Step S2604 and/or Step S2606, the configuration is changed back (reverted) to the configuration used in the handover source for a part or all of the radio bearers based on the fact that the first configuration is performed for the UE 122 and/or the fact that a radio link failure is not detected in the primary cell of the handover source, and in this case, processing of starting or restarting a part or all of the state variables by configuring the initial value without changing back (reverting) to the configuration or the state used in the handover source may be performed. The configuration is changed back (reverted) to the configuration used in the handover source for a part or all of the radio bearers based on the fact that the first configuration is performed for the UE 122 and/or the fact that a radio link failure is not detected in the primary cell of the handover source, and in this case, processing of starting or restarting the value of a part or all of the state variables by configuring the initial value without changing back (reverting) to the configuration or the state used in the handover source may be performed for the radio bearer to which the DAPS handover is not applied, or may be performed for the UM bearer to which the DAPS handover is not applied. The configuration is changed back (reverted) to the configuration used in the handover source for a part or all of the radio bearers based on the fact that the first configuration is performed for the UE 122 and/or the fact that a radio link failure is not detected in the primary cell of the handover source, and in this case, the radio bearer that performs the processing of starting or restarting the value of a part or all of the state variables by configuring the initial value without changing back (reverting) to the configuration or the state used in the handover source may be configured in advance by an RRC message. The part or all of the state variables may be a part or all of the state variables of the PDCP entity, may be a part or all of the state variables of the RLC entity, or may be a part or all of the state variables of the MAC entity.

In Step S2604 and/or Step S2606, PDCP entity of a part or all of the radio bearers may be caused to perform status report transmission and/or data recovery, based on the fact that the first configuration is performed for the UE 122 and/or the fact that a radio link failure is not detected in the primary cell of the handover source. The status report may be a status report described in NPL 5 and/or NPL 11. In other words, the status report may be a report for conveying the COUNT value of the PDCP SDU waiting to be received (the PDCP SDU that is not received yet) to the transmission side. The data recovery may be data recovery described in NPL 5 and/or NPL 11. In other words, the data recovery may be processing of retransmitting the PDCP Data PDU that has not received a notification of transmission success from the lower layer in the radio bearer (AM DRB) for which the RLC AM is configured or established. The processing of causing to perform the status report transmission and/or the data recovery in the PDCP entity of a part or all of the radio bearers based on the fact that the first configuration is performed for the UE 122 and/or the fact that a radio link failure is not detected in the primary cell of the handover source may be performed for the radio bearer to which the DAPS handover is applied. The processing of causing to perform the status report transmission and/or the data recovery in the PDCP entity of a part or all of the radio bearers based on the fact that the first configuration is performed for the UE 122 and/or the fact that a radio link failure is not detected in the primary cell of the handover source may be performed for the AM DRB to which the DAPS handover is applied.

Note that a part or all of the terms of “handover source” from Step S2600 to Step S2606 may be interpreted as a PCell of the handover source (PCell of the source), or may be interpreted as a cell group of the handover source (cell group of the source). A part or all of the terms of “handover target” from Step S2600 to Step S2606 may be interpreted as a PCell of the handover target (PCell of the target), or may be interpreted as a cell group of the handover target (cell group of the target).

Thus, in the embodiment of the present invention, efficient communication can be performed during handover of the UE 122.

Each of the radio bearers in the above description may be a DRB, may be an SRB, or may be a DRB and an SRB.

In the above description, the radio bearer to which the DAPS handover is applied may be the DRB to which the DAPS handover is applied. The radio bearer to which the DAPS handover is not applied may be the DRB to which the DAPS handover is not applied.

In the above description, expressions such as “linked,” “corresponding”, “associated,” and the like may be replaced with one another.

A part or all of the steps need not be performed in the examples of each processing or in the examples of the flows of each processing in the above description. The order of the steps may be different in the examples of each processing or in the examples of the flows of each processing in the above description. A part or all of the processing in each step need not be performed in the examples of each processing or in the examples of the flows of each processing in the above description. The order of processing in each step may be different in the examples of each processing or in the examples of the flows of each processing in the above description.

In the above description, “for MBB-HO” and/or “it is the MBB-HO” may be a case where transmission and/or reception of user data is performed in the target cell with continued transmission and/or reception of user data in the source cell in a case that in the LTE, RRC connection reconfiguration including MobilityControlInfo is performed or that in the NR, RRC reconfiguration including Reconfiguration With Sync is performed, or “for MBB-HO” and/or “it is the MBB-HO” may be expressed by another term meaning an equivalent operation. “For MBB-HO” and/or “it is the MBB-HO” may be a case where in the LTE or NR, a specific information element (e.g., the MakeBeforeBreak-r16 information element illustrated in FIGS. 10 to 13 and FIG. 21 and/or mbb-drb illustrated in FIGS. 20 to 22 ) is included in the RRC reconfiguration message. “For MBB-HO” and/or “it is the MBB-HO” may be a case where the time during which data communication between the terminal apparatus and the base station apparatus is prevented (disconnect time) is set to or set closer to zero milliseconds (0 msec), or another term meaning this may be used to express “for MBB-HO” and/or “it is the MBB-HO.”

In the above description, the “configuration for MBB-HO” may be a configuration for transmission and/or reception of user data performed in the target cell with continued transmission and/or reception of user data in the source cell in a case that in the LTE, RRC connection reconfiguration including MobilityControlInfo is performed or that in the NR, RRC reconfiguration including Reconfiguration With Sync is performed, or the “configuration for MBB-HO” may be expressed by another term meaning an equivalent configuration. The “configuration for MBB-HO” may be a case where in the LTE or NR, a specific information element (e.g., the MakeBeforeBreak-r16 information element illustrated in FIG. 10 to FIG. 13 and FIG. 21 and/or mbb-drb illustrated in FIG. 20 and FIG. 21 ) is included in the RRC reconfiguration message. “For MBB-HO” and/or “it is the MBB-HO” may be a case where the time during which data communication between the terminal apparatus and the base station apparatus is prevented (disconnect time) is set to or set closer to zero milliseconds (0 msec), or another term meaning this may be used to express “for MBB-HO” and/or “it is the MBB-HO.”

In the above description, “to be the make before break-handover (MBB-HO)” may include a case that the master cell group for the target is created, and is simultaneously present with the master cell group for the source. Further, “to be the MBB-HO” may be transmission and/or reception of user data performed in a target cell with continued transmission and/or reception of user data in a source cell in a part or all of the radio bearers configured for the terminal apparatus in a case that RRC connection reconfiguration including MobilityControlInfo is performed in LTE, or RRC reconfiguration including Reconfiguration With Sync is performed in NR, or may be expressed by another term meaning an equivalent processing. Further, “to be the MBB-HO” may be a fact that a specific first information element (for example, the MakeBeforeBreak-r16 information element illustrated in FIG. 10 to FIG. 13 and FIG. 21 ) is included in the message related to reconfiguration of RRC connection in LTE or NR. The radio bearer that performs transmission and/or reception of user data in the target cell with continued transmission and/or reception of user data in the source cell may be the radio bearer to which the make before break-handover is applied. The radio bearer to which the make before break-handover is applied may be a radio bearer indicated by a specific second information element (for example, mbb-drb illustrated in FIG. 20 to FIG. 21 ).

In the above description, the “make before break-handover (MBB-HO)” may be performing (Reduce User Data Interruption (RUDI)) processing in which the time during which data communication between the terminal apparatus and the base station apparatus is prevented (disconnect time) is set to or set closer to zero milliseconds (0 msec), or another term meaning this may be used to express “make before break-handover (MBB-HO).”

Note that in each embodiment of the present invention, the handover may be interpreted as Reconfiguration With Sync. For example, the make before break-handover may be interpreted as a make before break Reconfiguration With Sync.

Note that in the above description, “A may be interpreted as B” may include the meaning that B is interpreted as A in addition to interpretation of A as B. In a case that the above description contains “C may be D” and “C may be E,” this means inclusion of “D may be E.” In a case that the above description contains “F may be G” and “G may be H,” this means inclusion of “F may be H.”

In the above description, in a case that a condition “A” and a condition “B” are conflicting conditions, the condition “B” may be expressed as “other” condition of the condition “A”.

Various aspects of the terminal apparatus according to embodiments of the present invention will be described below.

(1) A first aspect of the present invention is a terminal apparatus for communicating with a base station apparatus, wherein in a case that a first timer expires, and a first failure is not detected, a second timer used for detecting loss of an RLC SDU in a reception side that is configured for an RLC entity of a first radio bearer is stopped and reconfigured, based on a fact that first configuration is performed for the terminal apparatus and a fact that second configuration is performed for the first radio bearer established for the terminal apparatus.

(2) The terminal apparatus according to (1), wherein in a case that the first timer expires, and the first failure is not detected, the terminal apparatus further stops and reconfigures a third timer used for retransmission of a poll in a transmission side, which is configured for the RLC entity of the first radio bearer, based on a fact that the first configuration is performed for the terminal apparatus, and a fact that the second configuration is performed for the first radio bearer established for the terminal apparatus.

(3) The terminal apparatus according to (1) or (2), wherein in a case that the first timer expires, and the first failure is not detected, the terminal apparatus further stops and reconfigures a fourth timer used for prohibiting transmission of a status PDU in a reception side, which is configured for the RLC entity of the first radio bearer, based on a fact that the first configuration is performed for the terminal apparatus, and a fact that the second configuration is performed for the first radio bearer established for the terminal apparatus.

(4) The first timer according to (1), (2), or (3) is a timer that is started in a case that the terminal apparatus receives an RRC reconnection message including an information element for indicating change of a serving cell in an RRC connected state from the base station apparatus, and that causes the terminal apparatus to reestablish RRC connection in a case that the first timer expires.

(5) The first failure according to (1), (2), or (3) is a radio link failure in a primary cell of a source.

(6) The first configuration according to (1), (2), or (3) is a configuration related to DAPS handover, and the second configuration is a configuration in which the DAPS handover is not applied to the first radio bearer.

(7) A second aspect of the present invention is a method of a terminal apparatus for communicating with a base station apparatus, the method including in a case that a first timer expires, and a first failure is not detected, stopping and reconfiguring a second timer used for detecting loss of an RLC SDU in a reception side that is configured for an RLC entity of a first radio bearer, based on a fact that first configuration is performed for the terminal apparatus and a fact that second configuration is performed for the first radio bearer established for the terminal apparatus.

(8) The method of the terminal apparatus according to (7) further includes, in a case that the first timer expires, and the first failure is not detected, stopping and reconfiguring a third timer used for retransmission of a poll in a transmission side, which is configured for the RLC entity of the first radio bearer, based on a fact that the first configuration is performed for the terminal apparatus, and a fact that the second configuration is performed for the first radio bearer established for the terminal apparatus.

(9) The method of the terminal apparatus according to (7) or (8) further includes, in a case that the first timer expires, and the first failure is not detected, stopping and reconfiguring a fourth timer used for prohibiting transmission of a status PDU in a reception side, which is configured for the RLC entity of the first radio bearer, based on a fact that the first configuration is performed for the terminal apparatus, and a fact that the second configuration is performed for the first radio bearer established for the terminal apparatus.

(10) The first timer according to (7), (8), or (9) is a timer that is started in a case that the terminal apparatus receives an RRC reconnection message including an information element for indicating change of a serving cell in an RRC connected state from the base station apparatus, and that causes the terminal apparatus to reestablish RRC connection in a case that the first timer expires.

(11) The first failure according to (7), (8), or (9) is a radio link failure in a primary cell of a source.

(12) The first configuration according to (7), (8), or (9) is a configuration related to DAPS handover, and the second configuration is a configuration in which the DAPS handover is not applied to the first radio bearer.

A program running on an apparatus according to an aspect of the present invention may serve as a program that controls a Central Processing Unit (CPU) and the like to cause a computer to operate in such a manner as to implement the functions of the above-described embodiments according to the present invention. Programs or the information handled by the programs are temporarily loaded into a volatile memory such as a Random Access Memory (RAM) while being processed, or stored in a non-volatile memory such as a flash memory, or a Hard Disk Drive (HDD), and then read, modified, and written by the CPU, as necessary.

Note that the apparatuses in the above-described embodiments may be partially enabled by a computer. In such a case, a program for realizing such control functions may be recorded on a computer-readable recording medium to cause a computer system to read the program recorded on the recording medium to perform the program. It is assumed that the “computer system” mentioned here refers to a computer system built into the apparatuses, and the computer system includes an operating system and hardware components such as a peripheral device. The “computer-readable recording medium” may be any of a semiconductor recording medium, an optical recording medium, a magnetic recording medium, and the like.

Moreover, the “computer-readable recording medium” may include a medium that dynamically retains a program for a short period of time, such as a communication line that is used to transmit the program over a network such as the Internet or over a communication line such as a telephone line, and may also include a medium that retains a program for a fixed period of time, such as a volatile memory within the computer system for functioning as a server or a client in such a case. Furthermore, the above-described program may be configured to realize some of the functions described above, and additionally may be configured to realize the functions described above, in combination with a program already recorded in the computer system.

Each functional block or various characteristics of the apparatuses used in the above-described embodiments may be implemented or performed with an electric circuit, that is, typically an integrated circuit or multiple integrated circuits. An electric circuit designed to perform the functions described in the present specification may include a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or other programmable logic devices, discrete gates or transistor logic, discrete hardware components, or a combination thereof. The general-purpose processor may be a microprocessor, or the processor may be a processor of known type, a controller, a micro-controller, or a state machine instead. The general-purpose processor or the above-mentioned circuits may include a digital circuit, or may include an analog circuit. In a case that with advances in semiconductor technology, a circuit integration technology appears that replaces the present integrated circuits, it is also possible to use an integrated circuit based on the technology.

Note that the invention of the present application is not limited to the above-described embodiments. Although apparatuses have been described as an example in the embodiment, the invention of the present application is not limited to these apparatuses, and is applicable to a stationary type or a non-movable type electronic apparatus installed indoors or outdoors such as a terminal apparatus or a communication apparatus, for example, an AV device, a kitchen device, a cleaning or washing machine, an air-conditioning device, office equipment, a vending machine, and other household appliances.

Although, the embodiments of the present invention have been described in detail above referring to the drawings, the specific configuration is not limited to the embodiments and includes, for example, design changes within the scope that does not depart from the gist of the present invention. Furthermore, in the present invention, various modifications are possible within the scope of claims, and embodiments that are made by suitably combining technical means disclosed according to the different embodiments are also included in the technical scope of the present invention. A configuration in which components, which are described in the embodiment described above, having similar effects are interchanged is also included in the present invention.

An aspect of the present invention can be utilized, for example, in a communication system, communication equipment (for example, a cellular phone apparatus, a base station apparatus, a wireless LAN apparatus, or a sensor device), an integrated circuit (for example, a communication chip), or a program. 

1. A terminal apparatus that communicates with a base station apparatus, the terminal apparatus comprising: a receiver configured to receive, from the base station apparatus, a Radio Resource Control (RRC) reconfiguration message; and a processor configured to perform configuration in accordance with the RRC reconfiguration message, wherein in a case that a first timer of an RRC protocol expires, a radio link failure in a source primary cell is not detected, a first configuration is included in the RRC reconfiguration message, and the first configuration is performed for the terminal apparatus, the processor reconfigures all state variables configured for a Radio Link Control (RLC) entity of a Signaling Radio Bearer (SRB) in the source primary cell to initial values, resumes the SRB suspended in the source primary cell, and transmits an RRC message for notifying the base station apparatus that Dual Active Protocol Stack (DAPS) handover has failed, and the first configuration is a configuration related to a radio bearer to which the DAPS handover is applied.
 2. The terminal apparatus according to claim 1, wherein the first timer starts in a case that the terminal apparatus receives, from the base station apparatus, an RRC message including an information element for indicating change of a serving cell in an RRC connected state, and stops in a case that a random access to a Special Cell (SpCell) succeeds.
 3. A base station apparatus that communicates with a terminal apparatus, the base station apparatus comprising: a transmitter configured to transmit, to the terminal apparatus, a Radio Resource Control (RRC) reconfiguration message; and a processor configured to cause the terminal apparatus to perform configuration in accordance with the RRC reconfiguration message, wherein in a case that a first timer of an RRC protocol expires, a radio link failure in a source primary cell is not detected, a first configuration is included in the RRC reconfiguration message, and the first configuration is performed for the terminal apparatus, the processor causes the terminal apparatus to reconfigure all state variables configured for a Radio Link Control (RLC) entity of a Signaling Radio Bearer (SRB) in the source primary cell to initial values, resume the SRB suspended in the source primary cell, and transmit an RRC message for notifying the base station apparatus that Dual Active Protocol Stack (DAPS) handover has failed, and the first configuration is a configuration related to a radio bearer to which the DAPS handover is applied.
 4. The base station apparatus according to claim 3, wherein the first timer starts in a case that the terminal apparatus receives, from the base station apparatus, an RRC message including an information element for indicating change of a serving cell in an RRC connected state, and stops in a case that a random access to a Special Cell (SpCell) succeeds.
 5. A method for a terminal apparatus that communicates with a base station apparatus, the method comprising: receiving, from the base station apparatus, a Radio Resource Control (RRC) reconfiguration message; performing configuration in accordance with the RRC reconfiguration message; and in a case that a first timer of an RRC protocol expires, a radio link failure in a source primary cell is not detected, a first configuration is included in the RRC reconfiguration message, and the first configuration is performed for the terminal apparatus, reconfiguring all state variables configured for a Radio Link Control (RLC) entity of a Signaling Radio Bearer (SRB) in the source primary cell to respective initial values, resuming the SRB suspended in the source primary cell, and transmitting an RRC message for notifying the base station apparatus that Dual Active Protocol Stack (DAPS) handover has failed, and the first configuration is a configuration related to a radio bearer to which the DAPS handover is applied. 6-8. (canceled) 